[NETFILTER]: Fix iptables compat hook validation

In compat mode, matches and targets valid hooks checks always successful due
to not initialized e->comefrom field yet. This patch separates this checks from
translation code and moves them after mark_source_chains() call, where these
marks are initialized.

Signed-off-by: Dmitry Mishin <dim@openvz.org>
Signed-off-by; Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>