networkmanager: fix detection of slow initialization modems

Some modems (e.g. the XBee Cellular LTE Cat 1) have a long initilization
process and are not available when ModemManager tries to detect them
on boot.

For those modems schedule a rescan a bit later after NetworkManager has
been launched, so they are detected properly.

https://jira.digi.com/browse/DEL-4661

Signed-off-by: Javier Viguera <javier.viguera@digi.com>

meta-digi-dey/recipes-connectivity/networkmanager/networkmanager/networkmanager-init

@@ -8,7 +8,7 @@ case "${1}" in
 	start)
 		mkdir -p /var/run/NetworkManager
 		echo -n "Starting ${DESC}: "
-		${DAEMON}
+		${DAEMON} && (sleep 40 && mmcli --scan-modems 1>/dev/null 2>&1) &
 		echo "done"
 		;;
 	stop)