mptcp: pm: add a build check for userspace_pm_dump_addr

mptcp: pm: add a build check for userspace_pm_dump_addr

This patch adds a build check for mptcp_userspace_pm_dump_addr() to make
sure there is enough space in 'cb->ctx' to store an address id bitmap.

Just in case info stored in 'cb->ctx' are increased later.

Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20250221-net-next-mptcp-pm-misc-cleanup-3-v1-3-2b70ab1cee79@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>