osmo_sccp_simple_client_on_ss7_id(): Fail to start a client on an ASP explicitly configured as sctp server

Right now, if a user configures an cs7 instance, as and asp (with
sctp-role server) in the VTY, then the function
osmo_sccp_simple_client_on_ss7_id() (used by osmo-bsc, osmo-msc,
osmo-hnbgw, etc.) will silently change the config to be SCTP client.
This is really confusing, since the user configured explicitly the ASP
as server but ends up running as client.
Instead, if the user explicitly configured the ASP as SCTP server,
return an error asking the user to apply changes to its config file.

Change-Id: I20de33edb8751a515d6719c49efadfc387dd85f8
---
M src/sccp_user.c
1 file changed, 24 insertions(+), 0 deletions(-)