Changes

Fix setting traffic-mode 'roundrobin' over VTY

String in osmo_ss7_as_traffic_mode_vals[] is "round-robin" while string
in VTY command was "roundrobin", so it didn't really match when set over
VTY. This has apparently broken for really long, I couldn't find the
originating commit breaking this.

Use "roundrobin" (without dash) to match wording used in Cisco ITP.

Change-Id: I61340549c596f1c04bc2269dbc165c327bf72037