Move adb_main to its own file.

Change-Id: If6e98c089b39f73bd8f4a878a82669bfeee367f3
diff --git a/adb/adb_auth.c b/adb/adb_auth.c
index 00cf469..11a89b0 100644
--- a/adb/adb_auth.c
+++ b/adb/adb_auth.c
@@ -26,6 +26,8 @@
 #include "adb_auth.h"
 #include "sysdeps.h"
 
+int auth_enabled = 0;
+
 void send_auth_request(atransport *t)
 {
     D("Calling send_auth_request\n");