net: ip_route_get: resolv hostnames ...

When global.net.server is a hostname instead of an IP address we have to
resolv it.

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

net: ip_route_get: Hook help text to command ...

The help text is present but not hooked into the command structure. Fix
this.

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

net: ip_route_get: Fix error message ...

We do getopt(), so the next argument is in argv[optind], not in argv[1].

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

commands: Add ip_route_add command ...

The ip_route_get command is used to retrieve the network
device used to reach a given IP address. This is useful
for informational purposes and also for the network boot
which wants to get the linux.bootargs parameter of the
network device used for nfsroot.

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