mqtt: tidy connect and dns
mqtt: tidy connect and dns

- Push the self-ref to after all allocations and error returns

- Don't try to extract IPv4 from the domain string ourselves, let the
  resolver, since it can

- Don't try to connect to localhost.  That can't possibly work.

nwf/nodemcu-firmware,nwf/nodemcu-firmware,nwf/nodemcu-firmware,nwf/nodemcu-firmware,nwf/nodemcu-firmware