Fix typo setting up certificate masks

The certificate masks are used to select which ciphersuite we are going to
use. The variables |emask_k| and |emask_a| relate to export grade key
exchange and authentication respecitively. The variables |mask_k| and
|mask_a| are the equivalent versions for non-export grade. This fixes an
instance where the two usages of export/non-export were mixed up. In
practice it makes little difference since it still works!
Reviewed-by: NRichard Levitte <levitte@openssl.org>

ssl/ssl_lib.c

@@ -2024,7 +2024,7 @@ void ssl_set_masks(SSL *s, const SSL_CIPHER *cipher)
     if (dh_dsa_export)
         emask_k |= SSL_kDHd;
 
-    if (emask_k & (SSL_kDHr | SSL_kDHd))
+    if (mask_k & (SSL_kDHr | SSL_kDHd))
         mask_a |= SSL_aDH;
 
     if (rsa_enc || rsa_sign) {