add voice_call_internal_mncc.msc

Same as voice_call_external_mncc.msc, but run with internal MNCC. Shows
some curious differences like the MNCC_LCHAN_MODIFY that internal MNCC
sends, but external doesn't.

Change-Id: Ic003322dc4e3fce24a8413688cfe18198a4dc08a
diff --git a/doc/sequence_charts/Makefile.am b/doc/sequence_charts/Makefile.am
index f71d934..7a52776 100644
--- a/doc/sequence_charts/Makefile.am
+++ b/doc/sequence_charts/Makefile.am
@@ -16,6 +16,7 @@
 	$(builddir)/inter_bsc_ho.png \
 	$(builddir)/inter_msc_ho.png \
 	$(builddir)/voice_call_external_mncc.png \
+	$(builddir)/voice_call_internal_mncc.png \
 	$(builddir)/call_reestablishment.png \
 	$(NULL)