userns: Convert xt_LOG to print socket kuids and kgids as uids and gids

xt_LOG always writes messages via sb_add via printk.  Therefore when
xt_LOG logs the uid and gid of a socket a packet came from the
values should be converted to be in the initial user namespace.

Thus making xt_LOG as user namespace safe as possible.

Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: Patrick McHardy <kaber@trash.net>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

init/Kconfig

@@ -945,7 +945,6 @@ config UIDGID_CONVERTED
 	depends on NET_9P = n
 	depends on NETFILTER_XT_MATCH_OWNER = n
 	depends on NETFILTER_XT_MATCH_RECENT = n
-	depends on NETFILTER_XT_TARGET_LOG = n
 	depends on AF_RXRPC = n
 	depends on NET_KEY = n
 	depends on DNS_RESOLVER = n