sig_ss7: Fix compiler warnings.

........

Merged revisions 400268 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@400269 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/sig_ss7.c

@@ -42,6 +42,7 @@
 #include "asterisk/musiconhold.h"
 #include "asterisk/cli.h"
 #include "asterisk/transcap.h"
+#include "asterisk/stasis_channels.h"
 
 #include "sig_ss7.h"
 #if defined(LIBSS7_ABI_COMPATIBILITY)