add bp-tools support for plain adb mode

On userdebug builds, only adb is brought up, not adb+mtp.
When booting into bp-tools mode on a userdebug device, no overlay
entry is present, which means the expected mode isn't entered.

Add an overlay entry.

Bug: 22062484
Change-Id: I2dd3b6064c2591dca595a216df9a37a11eab793c
diff --git a/overlay/frameworks/base/core/res/res/values/config.xml b/overlay/frameworks/base/core/res/res/values/config.xml
index b38c193..569769f 100644
--- a/overlay/frameworks/base/core/res/res/values/config.xml
+++ b/overlay/frameworks/base/core/res/res/values/config.xml
@@ -135,6 +135,7 @@
         <item>"bp-tools:rndis:rndis,diag,diag_mdm,serial_hsic,serial_tty,rmnet_hsic,usbnet,adb"</item>
         <item>"bp-tools:mtp,adb:diag,diag_mdm,serial_hsic,serial_tty,rmnet_hsic,usbnet,adb"</item>
         <item>"bp-tools:mtp:diag,diag_mdm,serial_hsic,serial_tty,rmnet_hsic,usbnet"</item>
+        <item>"bp-tools:adb:diag,diag_mdm,serial_hsic,serial_tty,rmnet_hsic,usbnet,adb"</item>
         <item>"mot-factory:rndis,adb:usbnet,adb"</item>
         <item>"mot-factory:rndis:usbnet"</item>
         <item>"mot-factory:mtp,adb:usbnet,adb"</item>