qcacld-2.0: Validate packet length, before processing PTT commands

propagation from qcacld-3.0 to qcacld-2.0.

There is a possibility of buffer overread while processing PTT
commands, because of packet length check is missing.

While processing PTT commands, validate packet length to make sure
there is no buffer overread.

CRs-Fixed: 2125577
Bug: 65853393
Signed-off-by: Srinivas Girigowda <sgirigow@codeaurora.org>