MINOR: ssl: Reorder struct certificate_ocsp members

Just swapping those two 'refcount' and 'response' members enables to
fill two 4 bytes holes in the structure.
diff --git a/include/haproxy/ssl_ocsp-t.h b/include/haproxy/ssl_ocsp-t.h
index 599d68a..4448431 100644
--- a/include/haproxy/ssl_ocsp-t.h
+++ b/include/haproxy/ssl_ocsp-t.h
@@ -42,8 +42,8 @@
 	struct ebmb_node key;
 	unsigned char key_data[OCSP_MAX_CERTID_ASN1_LENGTH];
 	unsigned int key_length;
-	struct buffer response;
 	int refcount;
+	struct buffer response;
 	long expire;
 	X509 *issuer;
 	STACK_OF(X509) *chain;