qcacmn: Clear the peer when it is deleted

The peer rx packets should be flushed when
deleting the peer and its state should be reset
to DISCONNECT, when deleting the peer.

If the state of peer is not set to DISCONNECT,
then the flushing of rx packets for the peer
which is being deleted will call the rx callback
and submit these packet to the stack, which can
cause unwanted behaviour.

This way the UMAC does not need to specifically
call clear peer before deleting the peer.

Change-Id: I3b5a737126350a361d968f6349aef6291b2e3f56
CRs-Fixed: 2659629