ss: Distinguish between IPv4 and IPv6 wildcard sockets

ss: Distinguish between IPv4 and IPv6 wildcard sockets

Commit aba9c23a6e1cb ("ss: enclose IPv6 address in brackets") unified
display of wildcard sockets in IPv4 and IPv6 to print the unspecified
address as '*'. Users then complained that they can't distinguish
between address families anymore, so change this again to what Stephen
Hemminger suggested:

| *:80    << both IPV6 and IPV4
| [::]:80 << IPV6_ONLY
| 0.0.0.0:80  << IPV4_ONLY

Note that on older kernels which don't support INET_DIAG_SKV6ONLY
attribute, pure IPv6 sockets will still show as '*'.

Cc: Humberto Alves <hjalves@live.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Phil Sutter <phil@nwl.cc>