mptcp: add mptcp_for_each_userspace_pm_addr macro

Similar to mptcp_for_each_subflow() macro, this patch adds a new macro
mptcp_for_each_userspace_pm_addr() for userspace PM to iterate over the
address entries on the local address list userspace_pm_local_addr_list
of the mptcp socket.

This patch doesn't change the behaviour of the code, just refactoring.

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/20241213-net-next-mptcp-pm-misc-cleanup-v1-2-ddb6d00109a8@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>