BTE: Allocate LogMsg buffer on the stack

Problem:
Due to static 1k buffer in LogMsg function is leading to a crash in
btapp as this function is called from multiple threads

Steps:
A2DP streaming or similar process that performs excessive logging

Failure: Crash occurs

Root Cause:
Static buffer being accessed and updated by different threads parallelly

Fix:
Used local buffer instead of static buffer from LogMsg function

Test: manual
Fixes: 69586278
Change-Id: I037d85c1ca0e134d1fa86308d0467f88d8ea159d