Add os if layer for CoAP(Constrained Application Protocol)
component. It provides interfaces to parse netlink messages
for vendor command QCA_NL80211_VENDOR_SUBCMD_COAP_OFFLOAD
and take action accordingly, including enable/disable offload
reply/periodic transmitting for CoAP messages, and fetching
CoAP messages those cached during offload processing.
Change-Id: Ibbf9baf3802d305f9989e024ce764a6071b1fc6b
CRs-Fixed: 3254541
