Enable multi-thread receiver support

This change implements locking on the receive and free
message rings such that multiple user threads can concurrently
invoke rmr receive functions.

Signed-off-by: E. Scott Daniels <daniels@research.att.com>
Change-Id: If012c5699e071f1d85f604c79baf8c4e8b77e94a
diff --git a/CHANGES b/CHANGES
index 976169f..f5d970d 100644
--- a/CHANGES
+++ b/CHANGES
@@ -2,6 +2,9 @@
 API and build change  and fix summaries. Doc correctsions
 and/or changes are not mentioned here; see the commit messages.
 
+2020 January 22; verison 3.0.3
+	Enable thread support for multiple receive threads.
+
 2020 January 21; verison 3.0.2
 	Fix bug in SI95 (missing reallocate payload function).