net: add missing READ_ONCE(sk->sk_rcvlowat) annotation

net: add missing READ_ONCE(sk->sk_rcvlowat) annotation

BugLink: https://bugs.launchpad.net/bugs/2038236
[ Upstream commit e6d12bdb435d23ff6c1890c852d85408a2f496ee ]

In a prior commit, I forgot to change sk_getsockopt()
when reading sk->sk_rcvlowat locklessly.

Fixes: eac66402d1c3 ("net: annotate sk->sk_rcvlowat lockless reads")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>