Fix buffer overflow in BRSF

bta_hf_client_at does not properly check bounds on its inputs,
allowing a buffer overflow when fed a buffer that is more than
twice the expected maximum size.  Add a new bounds check to
enforce, and a new security test to validate.

Bug: 231156521
Test: atest: BtaHfClientSecurityTest
Tag: #security
Ignore-AOSP-First: Security

Change-Id: I2cf89a786ba7cd0423eaccd8082bd824ac2f0d43
(cherry picked from commit f8adec66)
Merged-In: I2cf89a786ba7cd0423eaccd8082bd824ac2f0d43