wlan: Ignore CSA request for invalid channel

In present scenario, STA disconnects with AP if it receives
invalid channel in CSA IE. In this case STA shouldn't
disconnect with AP as this request may come from a spoof AP.

Ignore this CSA request as it might be from spoof AP and
if it is from genuine AP heart beat failure happens and
results in disconnection. After disconnection DUT may
reconnect to same or other APs

Change-Id: Iad99e1c8004b5060a2528ce7d4829badd2e0a3e0
CRs-Fixed: 3403638