The resolv() function used to return the IP address. When net_udp_new()
fails we return an error code though which the callers of resolv() take
as an IP address. This is wrong of course and we could return 0 in this
case. Instead we return an error code and pass the resolved IP as a
pointer which allows us to return proper error codes.

This patch also adds error messages and error returns to the various
callers of resolv() which used to just continue with a zero IP and
let the user figure out what went wrong.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>