osmo_sccp_simple_client_on_ss7_id(): Always follow VTY config of ASP if it was explicitly defined in VTY

The VTY config defaults are "role sg" and  "sctp-role server".
However, if not set explicitly in VTY,
osmo_sccp_simple_client_on_ss7_id() was replacing them to "role asp" and
"sctp-role client".
This is fine if the ASP is not defined/created at the VTY (aka
dynamically created with no config), but if the ASP is defined in the
VTY it becomes really confusing, since it's picking different defaults
than the usual ones.

Hence, follow always the same VTY defaults in
osmo_sccp_simple_client_on_ss7_id().

As a result of this change:
- Programs not defining the ASP over VTY keep the same behavior (ASP is
  created with role=asp and sctp-role=client)
- Programs defining ASP over VTY (eg. "asp asp-clnt-msc-0 5000 0 m3ua")
  explicitly setting "role" and "sctp-role": keep the same behavior
- Programs defining ASP over VTY but not explicitly setting "role" or
  "sctp-role", will get now the usual defaults instead.

So in summary, strange cases where osmo_sccp_simple_client_on_ss7_id()
is used (osmo-bsc, osmo-hnbgw, osmo-msc) and the dynamically created
ASP is created through VTY, then the config file must also explicitly
define the following lines:
role asp
sctp-role client

This patch also changes the "show running-config" VTY cmd to also always
show the configured role and sctp-role values, which are of vital
importance to understand a given setup.

Change-Id: Ie81987265118e48173211f88b27a006115dc62d4
---
M include/osmocom/sigtran/osmo_ss7.h
M src/osmo_ss7_vty.c
M src/sccp_user.c
M tests/vty/ss7_asp_test.vty
4 files changed, 49 insertions(+), 22 deletions(-)