mwan3: use procd for locking everywhere

Replace locks on /var/run/mwan3.lock with locks via procd.

This fixes a deadlock issue where mwan3 stop would have a procd
lock, but a hotplug script would have the /var/run/mwan3.lock

Locking can be removed from mwan3rtmon since:
1) procd will have sent the KILL signal to the process during
shutdown, so it will not add routes to already removed interfaces on
mwan3 shutdown and
2) mwan3rtmon checks if an interface is active based on the
mwan3_iface_in_<IFACE> entry in iptables, and the hotplug script
always adds this before creating the route table and removes it
before deleting the route table

Fixes github issue #13704
(https://github.com/openwrt/packages/issues/13704)

net/mwan3/files/etc/init.d/mwan3

@@ -31,8 +31,6 @@ start_service() {
 	mwan3_init
 	config_foreach start_tracker interface
 
-	mwan3_lock "command" "mwan3"
-
 	mwan3_update_iface_to_table
 	mwan3_set_connected_ipset
 	mwan3_set_custom_ipset
@@ -43,8 +41,6 @@ start_service() {
 	mwan3_set_policies_iptables
 	mwan3_set_user_rules
 
-	mwan3_unlock "command" "mwan3"
-
 	procd_open_instance rtmon_ipv4
 	procd_set_param command /usr/sbin/mwan3rtmon ipv4
 	procd_set_param respawn
@@ -61,8 +57,6 @@ start_service() {
 stop_service() {
 	local ipset rule IP IPTR IPT family table tid
 
-	mwan3_lock "command" "mwan3"
-
 	config_load mwan3
 	mwan3_init
 	config_foreach mwan3_interface_shutdown interface
@@ -108,7 +102,6 @@ stop_service() {
 
 	rm -rf $MWAN3_STATUS_DIR $MWAN3TRACK_STATUS_DIR
 
-	mwan3_unlock "command" "mwan3"
 }
 
 reload_service() {