When a data packet is sent via HTC, it is mapped before being inserted
into the TX queue. However, for control packets, the mapping is done
after being inserted into the queue. This leads to a situation where the
TX queue flush can unmap a pending control packet that was never mapped.
Make sure the TX flush function only unmaps packets that have previously
been mapped.
Change-Id: I48572fb34ae940923012d495625a33a00f74b9ed
CRs-Fixed: 2157006