apps/netutils/netlib: netlib_ipv[4|6]adaptor() will now use the new routing table interfaces if they are available: If the desination IP address does not correspond to the network served by any device, then the address of the router that should get us to the correct sub-net is is determined. Then the network adaptor that can communicate with the that router has the IP address that will returned.
apps/netutils/netlib: Add new utilities netlib_ipv[4|6]router() that can be used to determine the IP address of a router that would be used some some destination IP address that is not locally accessible.
apps/netutils/netlib: Add helpers for reading the routing table: netlib_read_ipv4route() and netlib_read_ipv6route()
