vxlan: Fix sparse warnings.

Fix following sparse warnings.
drivers/net/vxlan.c:238:44: warning: incorrect type in argument 3 (different base types)
drivers/net/vxlan.c:238:44:    expected restricted __be32 [usertype] value
drivers/net/vxlan.c:238:44:    got unsigned int const [unsigned] [usertype] remote_vni
drivers/net/vxlan.c:1735:18: warning: incorrect type in initializer (different signedness)
drivers/net/vxlan.c:1735:18:    expected int *id
drivers/net/vxlan.c:1735:18:    got unsigned int static [toplevel] *<noident>

Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>