gro: remove rcu_read_lock/rcu_read_unlock from gro_receive handlers

[ Upstream commit fc1ca334 ]

All gro_receive() handlers are called from dev_gro_receive()
while rcu_read_lock() has been called.

There is no point stacking more rcu_read_lock()

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 7e419693 ("fou: Fix null-ptr-deref in GRO.")
Signed-off-by: Sasha Levin <sashal@kernel.org>