sgsn: Add BSSGP_SIG port to ConnHdlr

So far, the ConnHdlr components were only able to exchange BSSGP PDUs
on the PTP BVC, but not on the SIGNALING BVC.  For this, we need to
actually connect to the BSSGP_SP_SIG that BSSGP_Emulation provides.

Change-Id: I4482a24e4808ac2fe04401224f628606d8207416
Related: OS#4616
1 file changed