not sending SIOS on remote link deactivation

[ivlovric]

Using libss7 2.0, Dahdi 3.0 and Asterisk 15.
In acceptance stage of project, we faced issue where our setup should send SIOS LSSU message when remote side deactivates slc link but it doesnt.

I assume correct sequence of messages is this according to T-REC-Q.781 MTP level 2 test spectfication:
----> SIOS
<---- start timer t2
<---- SIO
<---- SIOS (after timer T2 runs out)

More description of expected behaviour here:
http://lists.digium.com/pipermail/asterisk-ss7/2009-November/003212.html

--- ss7 debug ---
[1] Len = 4 [ 94 91 01 03 ]
[1] FSN: 17 FIB 1
[1] BSN: 20 BIB 1
[1] <[REMOTE-DPC:0] LSSU SIOS
[1]
[1] Link state change: INSERVICE -> IDLE
[1] Link state change: IDLE -> NOTALIGNED
[1] MTP3 T2 timer started on link SLC: 0 ADJPC: REMOTE-DPC
Linkset 1: Processing event: MTP2_LINK_DOWN
[Mar 4 13:58:35] WARNING[4005]: sig_ss7.c:1496 ss7_linkset: MTP2 link down (SLC 19)
[1] Len = 4 [ ff ff 01 00 ]
[1] FSN: 127 FIB 1
[1] BSN: 127 BIB 1
[1] >[REMOTE-DPC:0] LSSU SIO
[1]
[1] Len = 10 [ 98 94 07 80 00 b6 04 00 11 11 ]
[1] FSN: 20 FIB 1
[1] BSN: 24 BIB 1
[1] >[REMOTE-DPC:1] MSU
[1] [ 98 94 07 ]
[1] Network Indicator: 2 Priority: 0 User Part: NET_MNG (0)
[1] [ 80 ]
[1] OPC LOCAL-OPC DPC REMOTE-DPC SLS 0
[1] [ 00 b6 04 00 ]
[1] H0: 1 H1: 1
[1] Message type: COO
[1] [ 11 11 ]
[1]
[1] Len = 10 [ 94 99 07 80 12 00 80 0d 11 14 ]
[1] FSN: 25 FIB 1
[1] BSN: 20 BIB 1
[1] <[REMOTE-DPC:1] MSU
[1] [ 94 99 07 ]
[1] Network Indicator: 2 Priority: 0 User Part: NET_MNG (0)
[1] [ 80 ]
[1] OPC REMOTE-DPC DPC LOCAL-OPC SLS 0
[1] [ 12 00 80 0d ]
[1] H0: 1 H1: 1
[1] Message type: COO
[1] [ 11 14 ]
[1]
[Mar 4 13:58:36] ERROR[4005]: chan_dahdi.c:13672 dahdi_ss7_error: [1] Received message for slc 0x0, but we are 0x1. Dropping
[1] Len = 10 [ 94 9a 07 80 12 00 80 0d 21 14 ]
[1] FSN: 26 FIB 1
[1] BSN: 20 BIB 1
[1] <[REMOTE-DPC:1] MSU
[1] [ 94 9a 07 ]
[1] Network Indicator: 2 Priority: 0 User Part: NET_MNG (0)
[1] [ 80 ]
[1] OPC REMOTE-DPC DPC LOCAL-OPC SLS 0
[1] [ 12 00 80 0d ]
[1] H0: 1 H1: 2
[1] Message type: COA
[1] [ 21 14 ]
[1]
[Mar 4 13:58:36] ERROR[4005]: chan_dahdi.c:13672 dahdi_ss7_error: [1] Received message for slc 0x0, but we are 0x1. Dropping
[1] MTP3 T2 timer expired on link SLC: 0 ADJPC: REMOTE-DPC changeover completed
--- END ss7 debug ---