Reject ANDROID AT command if the first param is not String

The first parameter of ANDROID AT command indicates "type" which should
always be String.

Bug: 283725716
Test: atest BluetoothInstrumentationTests
(cherry picked from https://android-review.googlesource.com/q/commit:e255fcf5ed395b47c0baf8086ab896345bc3ae8d)
Merged-In: Ic7d11cf33562ccfca8321cdcfa0e4163614c4e0a
Change-Id: Ic7d11cf33562ccfca8321cdcfa0e4163614c4e0a