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