mptcp: drop unused sk in mptcp_get_options

[ Upstream commit 0799e21b ]

The parameter 'sk' became useless since the code using it was dropped
from mptcp_get_options() in the commit 8d548ea1 ("mptcp: do not set
unconditionally csum_reqd on incoming opt"). Let's drop it.

Signed-off-by: Geliang Tang <geliang.tang@suse.com>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: c1665273 ("mptcp: strict validation before using mp_opt->hmac")
Signed-off-by: Sasha Levin <sashal@kernel.org>