mgcp/rtp: Only patch timestamp alignment errors

Currently, all timestamps are force to SeqNo*d + C which is more than
required by the nanoBTS which seems to be sensitive to alignment
errors only (dTS != k*d, d = ptime * rate = 160).

This patch replaces the force_constant_timing feature by a
force_aligned_timing feature. The timestamp offset will only be
changed (and timestamp errors counted) when the alignment does not
match to the raster based on ptime (default 20ms).

The VTY interface does not change.

Sponsored-by: On-Waves ehf
diff --git a/openbsc/tests/mgcp/mgcp_test.c b/openbsc/tests/mgcp/mgcp_test.c
index 8b1b924..3cfc183 100644
--- a/openbsc/tests/mgcp/mgcp_test.c
+++ b/openbsc/tests/mgcp/mgcp_test.c
@@ -660,7 +660,7 @@
 	trunk.number_endpoints = 1;
 	trunk.endpoints = &endp;
 	trunk.force_constant_ssrc = patch_ssrc;
-	trunk.force_constant_timing = patch_ts;
+	trunk.force_aligned_timing = patch_ts;
 
 	endp.tcfg = &trunk;