net/mlx5e: Do not include rwlock.h directly

rwlock.h should not be included directly. Instead linux/splinlock.h
should be included. Including it directly will break the RT build.

Fixes: 549c243e ("net/mlx5e: Extract neigh-specific code from en_rep.c to rep/neigh.c")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Acked-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>