ipv4: remove sparse error in ip_neigh_gw4()

ipv4: remove sparse error in ip_neigh_gw4()

./include/net/route.h:373:48: warning: incorrect type in argument 2 (different base types)
./include/net/route.h:373:48:    expected unsigned int [usertype] key
./include/net/route.h:373:48:    got restricted __be32 [usertype] daddr

Fixes: 5e13fa575efc ("ipv4: Add helpers for neigh lookup for nexthop")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20220127013404.1279313-1-eric.dumazet@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>