Allow toggle of MTP debug

Via command line in TWRP:
twrp set tw_mtp_debug 1

This will enable debugging for MTP. You will need to disable and
re-enable MTP in order to see the debug logging.

Change-Id: Ia7bb0c584e10a4322b65ecf80a67ed7ee836b38e
diff --git a/mtp/twrpMtp.cpp b/mtp/twrpMtp.cpp
index ff58f79..6fe0ee3 100755
--- a/mtp/twrpMtp.cpp
+++ b/mtp/twrpMtp.cpp
@@ -68,7 +68,9 @@
 }
 #endif //def TWRPMTP
 
-twrpMtp::twrpMtp() {
+twrpMtp::twrpMtp(int debug_enabled = 0) {
+	if (debug_enabled)
+		MtpDebug::enableDebug();
 	mtpstorages = new storages;
 }