qcacld-3.0: Possible buffer overflow issue in wma

Possible bufer overflow risk in function
wmi_unified_bcn_tmpl_send.

Validate the beacon template length against
WMI_BEACON_TX_BUFFER_SIZE length to avoid overflow.

Change-Id: I98665de677f314f30a57991f48191f847718740c
CRs-Fixed: 2960714