BT: Airplane mode : Don't reset mEnableExternal in airplanemode

Issue:
BT turn on not happening after Airplane mode off

Steps:
 1. BT on
 2.Turn on airplane mode
 3.Turn off airplane mode

Repeat 2&3

Observed Result:
BT turn on not happening even airplane mode off

Expected Result:
BT turn on should be successful airplane mode off


RootCause:
When airplane mode turned on in BLE ON state, managerservice wrongly resets mEnableExternal.

Fix:
Don't reset mEnableExternal in airplanemode


Change-Id: I6859cc502e0751eed055d2d623a03f1c21b9c529
CRs-Fixed: 2573380