ipaddress: Fix and make consistent label match handling

ipaddress: Fix and make consistent label match handling

Since commit 9516823051ce ("ipaddress: Improve print_linkinfo()") we
return -1 instead of 0 when ip-address(8) label does not match network
device name as we did before change. This causes regression when trying
to output ip address matching label:

     # ip addr add 192.168.192.1/24 dev lo label lo:1
     # ip addr show label lo:1
     <no output>

This is special case and return 0 from print_linkinfo() earlier to match
only filter.ifindex and filter.up if given, but not rest fields in
@filter. Then call print_selected_addrinfo() without calling
print_link_stats() in ipaddr_list_flush_or_save().

Later print_selected_addrinfo() calls print_addrinfo() that finally
matches IFA_LABEL attribute in netlink buffer with filter.label using
ifa_label_match_rta().

On the other hand there is three conditions checked in print_linkinfo()
to determine label special case:

    1) filter.label != NULL
    2) filter.family == AF_UNSPEC || filter.family == AF_PACKET
    3) fnmatch(filter.label, name, 0)

With 1) it is ok to check if filtering by label is on by given pattern
in @filter.label.

Since label is IPv4 specific and AF_PACKET is for printing ip-link(8)
information (see ipaddr_link_list()::ipaddress.c as example) checking
for AF_PACKET in 2) doesn't take much sense: better to defer these
checks to print_addrinfo() determine valid combinations before calling
ifa_label_match_rta() to finally match IFA_LABEL to pattern in
filter.label.

For 3) we have following call for test case:

    fnmatch(pattern, string, flags) ->
      fnmatch(filter.label, name, 0) ->
        fnmatch("lo:1", "lo", 0) == FNM_NOMATCH (1) or non-zero on error

To support special case in print_linkinfo() for filtering by label we
only need to check if label pattern is given in filter.label and return
0 to skip print_link_stats() in ipaddr_list_flush_or_save(): actual
filtering will be done in print_addrinfo().

Before commit 9516823051ce ("ipaddress: Improve print_linkinfo()"):
-------------------------------------------------------------------

$ ip addr sh label lo
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN \
group default qlen 1000
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                                          fnmatch("lo", "lo", 0) == 0
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
$ ip addr show label 'lo:*'
    inet 192.168.192.1/24 scope global lo:1
       valid_lft forever preferred_lft forever
$ ip addr sh label lo:1
    inet 192.168.192.1/24 scope global lo:1
       valid_lft forever preferred_lft forever
$ ip -4 addr sh label lo:1
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN \
group default qlen 1000
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                                             filter.family == AF_INET
    inet 192.168.192.1/24 scope global lo:1
       valid_lft forever preferred_lft forever

After this change applied:
--------------------------

$ ip/ip addr show label lo
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
$ ip/ip addr show label 'lo:*'
    inet 192.168.192.1/24 scope global lo:1
        valid_lft forever preferred_lft forever
$ ip/ip addr show label lo:1
    inet 192.168.192.1/24 scope global lo:1
       valid_lft forever preferred_lft forever
$ ip/ip -4 addr show label lo:1
    inet 192.168.192.1/24 scope global lo:1
       valid_lft forever preferred_lft forever

Note that we no longer show link information as we did previously:
    we are filtering by "label" pattern, not showing by "dev".

Fixes: commit 9516823051ce ("ipaddress: Improve print_linkinfo()")
Reported-by: Vincent Bernat <vincent@bernat.im>
Signed-off-by: Serhey Popovych <serhe.popovych@gmail.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>