net/ncsi: Don't limit vids based on hot_channel

Currently we drop any new VLAN ids if there are more than the current
(or last used) channel can support. Most importantly this is a problem
if no channel has been selected yet, resulting in a segfault.

Secondly this does not necessarily reflect the capabilities of any other
channels. Instead only drop a new VLAN id if we are already tracking the
maximum allowed by the NCSI specification. Per-channel limits are
already handled by ncsi_add_filter(), but add a message to set_one_vid()
to make it obvious that the channel can not support any more VLAN ids.

Signed-off-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>