[tls] Include current time within the client random bytes

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/net/tls.c

 #include <stdlib.h>
 #include <stdarg.h>
 #include <string.h>
+#include <time.h>
 #include <errno.h>
 #include <byteswap.h>
 #include <ipxe/hmac.h>
 	tls_clear_cipher ( tls, &tls->tx_cipherspec_pending );
 	tls_clear_cipher ( tls, &tls->rx_cipherspec );
 	tls_clear_cipher ( tls, &tls->rx_cipherspec_pending );
-	tls->client_random.gmt_unix_time = 0;
+	tls->client_random.gmt_unix_time = time ( NULL );
 	if ( ( rc = tls_generate_random ( tls, &tls->client_random.random,
 			  ( sizeof ( tls->client_random.random ) ) ) ) != 0 ) {
 		goto err_random;