mgcp: Calculate the right Audio Processor resource for high endpoints

With this commit we can have more than 30 endpoints that will work. We
ignore the blocked endpoints 0x1 and 0x1f for each trunk and calculate
everything from the right start point.
diff --git a/include/mgcp/mgcp.h b/include/mgcp/mgcp.h
index 675db0c..2bd6eb5 100644
--- a/include/mgcp/mgcp.h
+++ b/include/mgcp/mgcp.h
@@ -122,7 +122,7 @@
 
 	/* Special MGW handling */
 	int target_trunk_start;
-	int trunk_base;
+	int voice_base;
 	int endp_offset;
 	int vad_enabled;