qahw: test: Pass correct channel mask and wave header length

Incorrect function is invoked to assign channel
mask value which resulted in passing incorrect
bytes of data to below layers. Fix the issue
by invoking correct function to assign proper
channel mask value.
Calculate wave header length with generic formula
instead of switch case.

Change-Id: I99e633eb10188dafca4e1a2320e06891b890d35a