Beef up unit tests for SI95 code

This changes adds some unit tests for SI95 modules which had none
prior, and extends some of the existing tests to improve coverage.

Issue-ID: RIC-777

Change-Id: I5d704776fd9094e8b17e35263cc4680bf822b38c
Signed-off-by: E. Scott Daniels <daniels@att.com>
diff --git a/test/mbuf_api_test.c b/test/mbuf_api_test.c
index 75d8445..bbace51 100644
--- a/test/mbuf_api_test.c
+++ b/test/mbuf_api_test.c
@@ -1,8 +1,8 @@
 // : vi ts=4 sw=4 noet :
 /*
 ==================================================================================
-	    Copyright (c) 2019 Nokia
-	    Copyright (c) 2018-2019 AT&T Intellectual Property.
+	    Copyright (c) 2019-2021 Nokia
+	    Copyright (c) 2018-2021 AT&T Intellectual Property.
 
    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
@@ -108,5 +108,5 @@
 		fprintf( stderr, "<OK>	 mbuf_api tests pass\n" );
 	}
 
-	return errors;
+	return !! errors;
 }