[INET]: Cleanup the xfrm4_tunnel_(un)register

Both check for the family to select an appropriate tunnel list.
Consolidate this check and make the for() loop more readable.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc net/ipv4/tunnel4.c
Simple merge