net: Add function to parse IP address string

The net_ipaddr_parse() will take a string with optional port
number and convert its information into struct sockaddr.
The format of the IP string can be:
     192.0.2.1:80
     192.0.2.42
     [2001:db8::1]:8080
     [2001:db8::2]
     2001:db::42

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>