charon-tkm: Claim to support SPIs on policies

This fixes rekeying as the delayed installation of the outbound SA
caused the nonce context to be expired already.

src/charon-tkm/src/tkm/tkm_kernel_ipsec.c

@@ -52,6 +52,12 @@ struct private_tkm_kernel_ipsec_t {
 
 };
 
+METHOD(kernel_ipsec_t, get_features, kernel_feature_t,
+	private_tkm_kernel_ipsec_t *this)
+{
+	return KERNEL_POLICY_SPI;
+}
+
 METHOD(kernel_ipsec_t, get_spi, status_t,
 	private_tkm_kernel_ipsec_t *this, host_t *src, host_t *dst,
 	uint8_t protocol, uint32_t *spi)
@@ -358,6 +364,7 @@ tkm_kernel_ipsec_t *tkm_kernel_ipsec_create()
 	INIT(this,
 		.public = {
 			.interface = {
+				.get_features = _get_features,
 				.get_spi = _get_spi,
 				.get_cpi = _get_cpi,
 				.add_sa  = _add_sa,