MINOR: peers: Do not emit global stick-table names.

MINOR: peers: Do not emit global stick-table names.

This commit "MINOR: stick-table: Add prefixes to stick-table names"
prepended the "peers" section name to stick-table names declared in such "peers"
sections followed by a '/' character.  This is not this name which must be sent
over the network to avoid collisions with stick-table name declared as backends.
As the '/' character is forbidden as first character of a backend name, we prefix
the stick-table names declared in peers sections only with a '/' character.
With such declarations:

    peers mypeers
       table t1

	backend t1
	   stick-table ... peers mypeers

at peer protocol level, "t1" declared as stick-table in "mypeers" section is different
of "t1" stick-table declared as backend.

In src/peers.c, only two modifications were required: use ->nid stktable struct
member in place of ->id in peer_prepare_switchmsg() to prepare the stick-table
definition messages. Same thing in peer_treat_definemsg() to treat a stick-table
definition messages.