interfaces: udp: Accept 0-byte payload packets

Using `<=` caused 0-byte payloads to be dropped, which was
unintended. This change ensures such packets are correctly processed.

Signed-off-by: Riho Natsushima <[email protected]>
Signed-off-by: Yasushi SHOJI <[email protected]>

Author: Nari-19

src/interfaces/csp_if_udp.c

@@ -46,7 +46,7 @@ int csp_if_udp_rx_work(int sockfd, size_t unused, csp_iface_t * iface) {
 	int header_size = csp_id_setup_rx(packet);
 	int received_len = recvfrom(sockfd, (char *)packet->frame_begin, sizeof(packet->data) + header_size, MSG_WAITALL, NULL, NULL);
 
-	if (received_len <= header_size) {
+	if (received_len < header_size) {
 		csp_buffer_free(packet);
 		return CSP_ERR_NOMEM;
 	}