mptcp: allow ADD_ADDR reissuance by userspace PMs

This change allows userspace PM implementations to reissue ADD_ADDR
announcements (if necessary) based on their chosen policy.
Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Kishen Maloor <kishen.maloor@intel.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/mptcp/pm_netlink.c

@@ -369,8 +369,16 @@ static bool mptcp_pm_alloc_anno_list(struct mptcp_sock *msk,
 
 	lockdep_assert_held(&msk->pm.lock);
 
-	if (mptcp_lookup_anno_list_by_saddr(msk, &entry->addr))
-		return false;
+	add_entry = mptcp_lookup_anno_list_by_saddr(msk, &entry->addr);
+
+	if (add_entry) {
+		if (mptcp_pm_is_kernel(msk))
+			return false;
+
+		sk_reset_timer(sk, &add_entry->add_timer,
+			       jiffies + mptcp_get_add_addr_timeout(net));
+		return true;
+	}
 
 	add_entry = kmalloc(sizeof(*add_entry), GFP_ATOMIC);
 	if (!add_entry)