LwIP: Add in TinyDTLS support

The dtls versions of the server and client are built as
server-dtls and client-dtls.

Add in flexible option support for server and client.  These are
a subset of the coap-server and coap-client options.

scripts/github_dist.sh

@@ -20,7 +20,7 @@ if test $err = 0 -a "x$ARCHIVE" != "x"; then
         make EXTRA_CFLAGS=-Werror && make install EXTRA_CFLAGS=-Werror
     err=$?
     if [ $err = 0 ] ; then
-        make -C $DIR/examples/lwip
+        make -C $DIR/examples/lwip EXTRA_CFLAGS=-Werror
         err=$?
     fi
     if [ $err = 0 ] ; then