channel scan: refactor APIs and triggers

README.md

src/cntlr.c

src/cntlr.h

src/cntlr_cmdu.c

src/cntlr_cmdu.h

src/cntlr_map.c

src/cntlr_tlv.c

src/cntlr_tlv.h

src/cntlr_ubus.c