[Xorp-hackers] Format output for showing network interface info

[Pavlin Radoslavov]

FYI, I just reimplemented the "show_interface" binary program
to use Orion's libfeaclient to obtain the network interface
information from the FEA (instead of the old ifmgr/0.1 XRL
interface).

The "show_interface" program is used by xorpsh to print the network
interfaces info. After some cleanup and modification of its output
format (which is based on the FreeBSD's "ifconfig" output), now the
output is like:

lo0/lo0: Flags:<ENABLED,MULTICAST,LOOPBACK> mtu 16384
        inet6 ::1 prefixlen 128
        inet6 fe80::1 prefixlen 64
        inet 127.0.0.1 subnet 127.0.0.0/8
        physical index 5
rl0/rl0: Flags:<ENABLED,BROADCAST,MULTICAST> mtu 1500
        inet6 fe80::111:2222:3333:4444 prefixlen 64
        inet 123.123.123.12 subnet 123.123.123.0/24 broadcast 123.123.123.255
        physical index 1
        ether 00:10:aa:bb:cc:dd
tun0/tun0: Flags:<ENABLED,MULTICAST,POINTTOPOINT> mtu 1300
        inet6 fe80::111:2222:3333:4444 prefixlen 64
        inet 10.30.30.1 subnet 10.30.30.1/32 --> 10.30.30.2
        physical index 6

Please let me know if the above format should look differently or
whether it needs some tweaks.

Thanks,
Pavlin