BUG/MINOR: peers: forget the remote table when ignoring an unknown key type

BUG/MINOR: peers: forget the remote table when ignoring an unknown key type

Commit 1696cfaa1 ("BUG/MEDIUM: peers: enforce check on incoming table key
type") makes peer_treat_definemsg() ignore a table definition with an
unknown key type. But contrary to all other paths ignoring a definition,
it leaves p->remote_table set to the local table matched by name. The
update messages which follow are thus not ignored but decoded using the
local table's key type and applied to it, while they were built for a
different key type. This is precisely the situation the commit wanted to
cover (a newer peer supporting new key types).

Let's reset p->remote_table as the other paths do.

HAProxy never emits such a value: peer_net_key_type[] only covers the five
supported key types, so a compliant peer stays below PEER_KT_TYPES. This is
therefore latent today, and becomes reachable the day a new key type is
added, when a newer peer talks to an older one in a mixed-version cluster.

This must be backported to all stable versions.