Move the listener code into its own file.

Change-Id: I7332455ed1a213daedeaa4a81260edf08b2fd131
diff --git a/adb/Android.mk b/adb/Android.mk
index 51318ef..702300b 100644
--- a/adb/Android.mk
+++ b/adb/Android.mk
@@ -16,6 +16,7 @@
 # get enough of adb in here that we no longer need minadb. https://b/17626262
 LIBADB_SRC_FILES := \
     adb_auth.c \
+    adb_listeners.c \
     transport.c \
     transport_usb.c \