package/comgt: Handle bind/unbind events

This script was expecting only add/remove events which has not been the
case since Kernel 4.12 (which added bind/unbind). Bind events were getting
treated as remove events which would cause hotplugged 3g modems to not
work.

More info:
https://lkml.org/lkml/2018/12/23/128
https://github.com/systemd/systemd/issues/8221

Signed-off-by: Arjun AK <arjunak234@gmail.com>
(cherry picked from commit 89ef883b92b3a87d9ab1bd289de26b9e72681dac)

package/network/utils/comgt/files/3g.usb

@@ -23,6 +23,8 @@ find_3g_iface() {
 	fi
 }
 
+[ "$ACTION" = add ] || [ "$ACTION" = remove ] || exit 0
+
 case "$DEVICENAME" in
 	tty*)
 		[ -e "/dev/$DEVICENAME" ] || [ "$ACTION" = remove ] || exit 0