ip: fix oneline output

ip: fix oneline output

Ip tool oneline option should output each record on a single line. While
oneline option is active the variable _SL_ replaces line feeds with the
'\' character. However, at the end of print_linkinfo() the variable _SL_
shouldn't be used, otherwise the whole output is on a single line.

Before this fix:
$ip -o link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode
DEFAULT group default qlen 1000\    link/loopback 00:00:00:00:00:00 brd
00:00:00:00:00:00\2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500
qdisc fq_codel state UP mode DEFAULT group default qlen 1000\
link/ether 52:54:00:60:0a:db brd ff:ff:ff:ff:ff:ff\3: eth1:
<BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode
DEFAULT group default qlen 1000\    link/ether 00:50:56:1b:05:cd brd
ff:ff:ff:ff:ff:ff\

After this fix:
$ip -o link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode
DEFAULT group default qlen 1000\    link/loopback 00:00:00:00:00:00 brd
00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state
UP mode DEFAULT group default qlen 1000\    link/ether 52:54:00:60:0a:db
brd ff:ff:ff:ff:ff:ff
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state
UP mode DEFAULT group default qlen 1000\    link/ether 00:50:56:1b:05:cd
brd ff:ff:ff:ff:ff:ff

Fixes: 3aa0e51be64b ("ip: add support for alternative name addition/deletion/list")
Signed-off-by: Moshe Shemesh <moshe@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David Ahern <dsahern@gmail.com>