qcacld-3.0: Remove interface up dependency for usable channels

Currently for QCA_NL80211_VENDOR_SUBCMD_USABLE_CHANNELS vendor
command STA interface should be UP and running. During STA/SAP
concurrency when STA is disabled SAP cannot get the usable channels
from driver since STA iface is brought down by Wifi HAL.

These changes remove interface running dependency for get usable
channels vendor command.

Change-Id: I3760adda2ce258f428f2b803112ab25503e97b60
CRs-Fixed: 3517894