Changes

sccp: Let some time for SCCP RLC to reach IUT before finishing test

Otherwise tear down of the test component immediatelly afterwards
creates a race condition where sometimes the RLC message is not sent
before closing the socket.
As a result, the SCCP-SCOC stays in DISCONN_PEND until T(rel) fires a
while afterwards, generating a new RLSD in a follow-up test, disrupting
expectancies of that unrelated test.

Since sccp_demo_user doesn't implement a Layer Manager, the recv() 0
from the socket doesn't automatically tear down the SCCP conn, since it
could have several ASPs:
"""
0: asp-asp-srv-client: ss7_asp_xua_srv_conn_rx_cb(): sctp_recvmsg() returned 0 (flags=0x80)
...
asp-srv-client: connection closed
XUA_ASP(asp-srv-client){ASP_ACTIVE}: Received Event SCTP-COMM_DOWN.ind
XUA_ASP(asp-srv-client){ASP_ACTIVE}: state_chg to ASP_DOWN
XUA_AS(as-srv-client){AS_ACTIVE}: Received Event ASPAS-ASP_DOWN.ind
XUA_AS(as-srv-client){AS_ACTIVE}: state_chg to AS_PENDING
Delivering N-PCSTATE.indication to SCCP User 'SCCP Management'
Ignoring SCCP user primitive N-PCSTATE.indication
[Here same 2 lines for SCCP User 'refuser', 'echo', 'callback', 'test_client_vty']
XUA_ASP(asp-srv-client){ASP_DOWN}: No Layer Manager, dropping M-ASP_DOWN.indication
XUA_ASP(asp-srv-client){ASP_DOWN}: No Layer Manager, dropping M-SCTP_RELEASE.indication
"""

Change-Id: Id7d5970bb0fe0e42fedcb56fe4a738a92ddd5bbf