Changes

*/osmo-stp.cfg: Explicitly define role & sctp-role

It was recently decided it's a good practice to always specify the role
and sctp-role for all ASPs configured in the VTY, since it's an
important configuration providing feedback on the network setup
expectancies.

Change-Id: Ia495bc3c5dd4421e5730c74b2f5dc4e4cdc1a673