net: tcp_probe: add IPv6 support

The tcp_probe currently only supports analysis of IPv4 connections.
Therefore, it would be nice to have IPv6 supported as well. Since we
have the recently added %pISpc specifier that is IPv4/IPv6 generic,
build related sockaddress structures from the flow information and
pass this to our format string. Tested with SSH and HTTP sessions
on IPv4 and IPv6.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>