src: add udev watcher to improve modem recovery

Most of the modem issues follow a (incomplete) USB device reset. Instead 
of relying solely on the existing timer, this patch adds a udev monitor 
which resets the modem as soon as its associated USB device is reset, 
which greatly improves recovery time.

meson.build

@@ -43,6 +43,7 @@ endif
 mgr_deps = [
     dependency('glib-2.0'),
     dependency('gio-unix-2.0'),
+    dependency('gudev-1.0'),
     dependency('libgpiod'),
     dependency('libusb-1.0'),
     dependency('mm-glib'),