MINOR: connection: use attach-srv name as SNI reuse parameter on reverse

MINOR: connection: use attach-srv name as SNI reuse parameter on reverse

On connection passive reverse from frontend to backend, its hash node is
calculated to be able to select it from the idle server pool. If
attach-srv rule defined an associated name, reuse it as the value for
SNI prehash.

This change allows a client to select a reverse connection by its name
by configuring its server line with a SNI to permit this.