vxlan: use htonl when snooping for loopback address

Currently "bridge fdb show dev vxlan0" lists loopback address as
"1.0.0.127". Using htonl(INADDR_LOOPBACK) rather than passing it
directly to vxlan_snoop fixes the problem.

Signed-off-by: Mike Rapoport <mike.rapoport@ravellosystems.com>
Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>