Actually use the READ_TIMEOUT_MS in the sample DTLS client and server

Signed-off-by: Ryan LaPointe <ryan@ryanlapointe.org>
diff --git a/ChangeLog.d/dtls_sample_use_read_timeout.txt b/ChangeLog.d/dtls_sample_use_read_timeout.txt
new file mode 100644
index 0000000..e3150d6
--- /dev/null
+++ b/ChangeLog.d/dtls_sample_use_read_timeout.txt
@@ -0,0 +1,2 @@
+Changes
+   * Fix the setting of the read timeout in the DTLS sample programs.