src: watch ofono service for new modem

If system is using ofono, use ofono dbus service to figure out the
modem's USB id.

src/libgdbofono/dbus-introspect.sh

@@ -0,0 +1,11 @@
+#!/bin/bash
+
+DEST="$1"
+OBJ_PATH="$2"
+METHOD="$3"
+shift 3
+
+dbus-send "$@" --print-reply --dest="$DEST" "$OBJ_PATH" "$METHOD" | \
+    grep -v '^method return' | \
+    sed -e 's/^[[:space:]]\+string "</</' \
+        -e 's_</node>"_</node>_'