Define MODP_CUSTOM constructors as variadic functions

They now match the dh_constructor_t signature.  This is a follow up for
the changes merged with b668bf3f9e and should fix use of MODP_CUSTOM on
Apple's ARM64 platform.

src/libstrongswan/plugins/pkcs11/pkcs11_dh.c

@@ -415,13 +415,15 @@ static chunk_t ecparams_lookup(diffie_hellman_group_t group)
 /**
  * Described in header.
  */
-pkcs11_dh_t *pkcs11_dh_create(diffie_hellman_group_t group,
-							  chunk_t g, chunk_t p)
+pkcs11_dh_t *pkcs11_dh_create(diffie_hellman_group_t group, ...)
 {
 	switch (group)
 	{
 		case MODP_CUSTOM:
 		{
+			chunk_t g, p;
+
+			VA_ARGS_GET(group, g, p);
 			return create_modp(group, p.len, g, p);
 		}
 		case ECP_192_BIT:

src/libstrongswan/plugins/pkcs11/pkcs11_dh.h

@@ -40,12 +40,10 @@ struct pkcs11_dh_t {
  * Creates a new pkcs11_dh_t object.
  *
  * @param group			Diffie Hellman group number to use
- * @param g				generator in case group is MODP_CUSTOM
- * @param p				prime in case group is MODP_CUSTOM
+ * @param ...			expects generator and prime as chunk_t if MODP_CUSTOM
  * @return				pkcs11_dh_t object, NULL if not supported
  */
-pkcs11_dh_t *pkcs11_dh_create(diffie_hellman_group_t group,
-							  chunk_t g, chunk_t p);
+pkcs11_dh_t *pkcs11_dh_create(diffie_hellman_group_t group, ...);
 
 #endif /** PKCS11_DH_H_ @}*/