Appease -Werror=maybe-uninitialized

test/bad_dtls_test.c: In function 'validate_client_hello':
test/bad_dtls_test.c:128:33: error: 'u' may be used uninitialized in this function [-Werror=maybe-uninitialized]
     if (!PACKET_get_1(&pkt, &u) || u != SSL3_RT_HANDSHAKE)
                                 ^
Apparently -O1 does not perform sufficient optimization to ascertain
that PACKET_get_1 will always initialize u if it returns true.
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4518)

test/bad_dtls_test.c

@@ -118,7 +118,7 @@ static int validate_client_hello(BIO *wbio)
     long len;
     unsigned char *data;
     int cookie_found = 0;
-    unsigned int u;
+    unsigned int u = 0;
 
     len = BIO_get_mem_data(wbio, (char **)&data);
     if (!PACKET_buf_init(&pkt, data, len))