Changes

xua_asp_fsm: Validate remote ASP Id matching config in SG role

The node in SG role really doesn't have an ASP Id of its own (it is
never sent over the wire). Hence, use the "asp-identifier <N>" VTY
config in SG role to require the ASP to identift itself with a given
ASP identifier.

Related: OS#6953
Change-Id: I3e22439aa7e22f7a6113b093c44ace6745c808b9