Validate all AVRCP packets before use to prevent out of bounds reads.

If a packet arrives that is too short to read all the fields from, then
an out of bounds read occurs. This patch validates all recieved packets
before use.

Bug: 119562595
Test: run net_test_avrcp
Change-Id: Ifc1c0def1b411664facbbeb7e4d6e9c56ecc31c1