ofproto: generate OFPXMT_OFB_ and OXM_OF_ from a single source
binary <-> text conversion of mac/ipv4/ipv6 addresses

implemented as a simple wrapper of netaddr.
replace homegrown bin<->text routines with addrconv
use bytes instead of int to represent ipv4 addresses

change ipv4 representation from int to bytes in many places.
replace homegrown bin<->text routines with addrconv for ipv4_to_{str,bin}.