inet: frag , remove an empty ifdef.

This patch removes an empty ifdef from inet_frag_intern()
in net/ipv4/inet_fragment.c.

commit b67bfe0d
(hlist: drop the node parameter from iterators) removed hlist from
net/ipv4/inet_fragment.c, but did not remove the enclosing ifdef command,
which is now empty.

Signed-off-by: Rami Rosen <ramirose@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>