To extend arp command fuctionality

[MikhailKasimov]

Hello!

The arp [options] <ifname> <IP> string from wicked --help hints the idea to extend wicked arp command to have the similar logic due to arp command.

1. wicked arp --cache-list <ifname>|all (analog to arp -a: display (all) hosts in alternative (BSD) style).

2. wicked arp --delete <IP>|all (analog to arp -d|--delete: delete a specified entry, will delete LLADDR parameter from /etc/sysconfig/network/ifcfg-<ifname>).

3. wicked arp --set <IP> <LLADDR> (analog to arp -s|--set: set a new ARP entry, will add LLADDR parameter to /etc/sysconfig/network/ifcfg-<ifname> or will replace, if LLADDR parameter is already exist in /etc/sysconfig/network/ifcfg-<ifname>).

Thanks!

[mtomaschewski]

See issue #690 -- we've added them for internal use "keeping door open" to extend when needed,
but there is no plan to do anything / extend to provide full functionality, because there are enough
utilities doing it, see also "man ip-neighbour", which handles both, ipv4 + ipv6.