[lwip-users] update ARP table

[Dmitry Potapov]

Hello everyone,

I have noticed that in lwIP 1.2.0 update of the ARP table on incoming
IP packets was disabled with the following comments:
/* CSi disabled ARP table update on ingress IP packets.
  This seems to work but needs thorough testing. */

I suppose there was a good reason to do so, but I would like to know
it. Was that performance concerns or something more serious?

Also, it looks like etharp_ip_input() is no longer used anywhere, so I
suppose it should be also commented out to reduce code footprint.

Dmitry