BUG/MINOR: peers: Wrong "new_conn" value for "show peers" CLI command.

BUG/MINOR: peers: Wrong "new_conn" value for "show peers" CLI command.

This counter could be hugely incremented by the peer task responsible of managing
peer synchronizations and reconnections, for instance when a peer is not reachable
there is a period where the appctx is not created. If we receive  stick-table
updates before the peer session (appctx) is instantiated, we reach the code
responsible of incrementing the "new_conn" counter.
With this patch we increment this counter only when we really instantiate a new
peer session thanks to peer_session_create().

May be backported as far as 2.0.