Rename diffie_hellman_t to key_exchange_t and change the interface etc.

This makes it more generic so we can use it for QSKE methods.

src/libstrongswan/crypto/transform.h

@@ -33,7 +33,7 @@ enum transform_type_t {
 	ENCRYPTION_ALGORITHM = 1,
 	PSEUDO_RANDOM_FUNCTION = 2,
 	INTEGRITY_ALGORITHM = 3,
-	DIFFIE_HELLMAN_GROUP = 4,
+	KEY_EXCHANGE_METHOD = 4,
 	EXTENDED_SEQUENCE_NUMBERS = 5,
 	HASH_ALGORITHM = 256,
 	RANDOM_NUMBER_GENERATOR = 257,