botan: Replace deprecated FFI function calls

Several "wrapper" functions have been marked deprecated with 2.11.0.

src/libstrongswan/plugins/botan/botan_ec_diffie_hellman.c

@@ -211,7 +211,7 @@ botan_ec_diffie_hellman_t *botan_ec_diffie_hellman_create(
 		return NULL;
 	}
 
-	if (botan_privkey_create_ecdh(&this->key, rng, this->curve_name))
+	if (botan_privkey_create(&this->key, "ECDH", this->curve_name, rng))
 	{
 		DBG1(DBG_LIB, "ECDH private key generation failed");
 		botan_rng_destroy(rng);