Add vendor command QCA_NL80211_VENDOR_SUBCMD_COAP_OFFLOAD to
enable/disable offload processing in firmware for CoAP messages
(RFC7252: The Constrained Application Protocol) or fetch the
CoAP messages cached during offload processing.
Change-Id: I2eaeba58ec6bc44738f68eb00c36ebdce2eae6f8
CRs-Fixed: 3193633