udpsclient: size the TCP receive buffer from max_packet_bytes so large MARTe frames are not dropped

A TCP frame is never fragmented; a real TCPStreamer cycle (240 KB) exceeded the UDP datagram
limit and made the client reconnect forever, seeing CONFIG but never DATA.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

deps/udpsclient/udps_client.c

@@ -198,6 +198,7 @@ struct udps_client {
     size_t                vals_cap;
 
     uint8_t *rxbuf;
+    size_t   rxbuf_cap;   /**< bytes allocated for rxbuf */
 
     udps_held_t held[UDPS_REORDER_SLOTS];
     size_t      held_bytes;    /**< payload bytes currently held */
@@ -1256,7 +1257,7 @@ static int read_tcp_frame(udps_client_t *c) {
     if (udps_parse_header(c->rxbuf, UDPS_HEADER_SIZE, &h) != 0) {
         return -1; /* desynchronised: the stream cannot be resynced */
     }
-    if (h.payload_bytes > (uint32_t)(UDPS_RX_BUF_BYTES - UDPS_HEADER_SIZE)) {
+    if (h.payload_bytes > c->rxbuf_cap - UDPS_HEADER_SIZE) {
         return -1;
     }
     if (h.payload_bytes > 0u &&
@@ -1350,7 +1351,13 @@ udps_client_t *udps_client_create(const udps_client_config_t *cfg) {
         return NULL;
     }
 
-    c->rxbuf = (uint8_t *)malloc(UDPS_RX_BUF_BYTES);
+    /* A UDP datagram is at most UDPS_MAX_DATAGRAM_BYTES; a TCP frame is not fragmented
+     * and may be as large as max_packet_bytes (MARTe's TCPStreamer allows 1 MiB). */
+    c->rxbuf_cap = UDPS_RX_BUF_BYTES;
+    if (c->cfg.use_tcp && (size_t)c->cfg.max_packet_bytes + UDPS_HEADER_SIZE > c->rxbuf_cap) {
+        c->rxbuf_cap = (size_t)c->cfg.max_packet_bytes + UDPS_HEADER_SIZE;
+    }
+    c->rxbuf = (uint8_t *)malloc(c->rxbuf_cap);
     if (c->rxbuf == NULL) {
         free(c);
         return NULL;