mptcp: mark ops structures as ro_after_init

stable inclusion
from stable-v5.10.163
commit 5aa15a8400cc3f05e7884975f29fa0c1f9362f2e
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7PJ9N

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5aa15a8400cc3f05e7884975f29fa0c1f9362f2e



----------------------------------------------------

From: Florian Westphal <fw@strlen.de>

commit 51fa7f8e upstream.

These structures are initialised from the init hooks, so we can't make
them 'const'.  But no writes occur afterwards, so we can use ro_after_init.

Also, remove bogus EXPORT_SYMBOL, the only access comes from ip
stack, not from kernel modules.

Cc: stable@vger.kernel.org # 5.10
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: zhaoxiaoqiang11 <zhaoxiaoqiang11@jd.com>