datatype: fix table listing if name resolution is not available

datatype: fix table listing if name resolution is not available

nft list table filter returns garbage here for IP and IPv6 addresses if
no name resolution is available. The output looks good if `-n' is used
in that case.

The problem is that getnameinfo() returns:

EAI_AGAIN   -3    /* Temporary failure in name resolution.  */

Without working name resolution. To fix this, force a fall back to
numeric resolution in that case.

While at it, fix also possible resolution of services in case of
that /etc/services is missing in the system.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>