feat(esp_netif): PPP: Use RAM allocated pbufs instead of POOL (fixed size)

PPP netif: Used allocated packet buffers of exact size
for input to TCP/IP stack to consume less memory in download mode
(compared to the previously used fixed sized packet buffers)

components/esp_netif/lwip/netif/ppp.c

@@ -0,0 +1,28 @@
+/*
+ * SPDX-FileCopyrightText: 2001-2004 Swedish Institute of Computer Science
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * SPDX-FileContributor: 2023 Espressif Systems (Shanghai) CO LTD
+ */
+#include "pppif.h"
+#include "lwip/tcpip.h"
+
+/*
+ * Similar to pppos_input_tcpip() from lwip's ppp netif, but instead
+ * of PBUF_POOL, we use PBUF_RAM type of the pbuf we pass to the stack
+ */
+err_t pppos_input_tcpip_as_ram_pbuf(ppp_pcb *ppp, u8_t *s, int l)
+{
+    struct pbuf *p = pbuf_alloc(PBUF_RAW, l, PBUF_RAM);
+    if (!p) {
+        return ERR_MEM;
+    }
+    pbuf_take(p, s, l);
+
+    err_t err = tcpip_inpkt(p, ppp_netif(ppp), pppos_input_sys);
+    if (err != ERR_OK) {
+        pbuf_free(p);
+    }
+    return err;
+}