PPP, add PPPoS CB for PPPoS private data

Created a new PPPoS CB going to have PPPoS private data, so allocating a
PPPoE or a PPPoL2TP interface does not allocate as well PPPoS variables.

src/include/lwip/memp_std.h

@@ -102,6 +102,9 @@ LWIP_MEMPOOL(LOCALHOSTLIST,  MEMP_NUM_LOCALHOSTLIST,   LOCALHOSTLIST_ELEM_SIZE,
 
 #if PPP_SUPPORT
 LWIP_MEMPOOL(PPP_PCB,       MEMP_NUM_PPP_PCB,              sizeof(ppp_pcb),             "PPP_PCB")
+#if PPPOS_SUPPORT
+LWIP_MEMPOOL(PPPOS_PCB,     MEMP_NUM_PPPOS_INTERFACES,     sizeof(pppos_pcb),           "PPPOS_PCB")
+#endif /* PPPOS_SUPPORT */
 #if PPPOE_SUPPORT
 LWIP_MEMPOOL(PPPOE_IF,      MEMP_NUM_PPPOE_INTERFACES,     sizeof(struct pppoe_softc),  "PPPOE_IF")
 #endif /* PPPOE_SUPPORT */

src/include/lwip/opt.h

@@ -416,6 +416,14 @@
 #define MEMP_NUM_PPP_PCB       1
 #endif
 
+/**
+ * MEMP_NUM_PPPOS_INTERFACES: the number of concurrently active PPPoS
+ * interfaces (only used with PPPOS_SUPPORT==1)
+ */
+#ifndef MEMP_NUM_PPPOS_INTERFACES
+#define MEMP_NUM_PPPOS_INTERFACES       MEMP_NUM_PPP_PCB
+#endif
+
 /**
  * MEMP_NUM_PPPOE_INTERFACES: the number of concurrently active PPPoE
  * interfaces (only used with PPPOE_SUPPORT==1)

src/include/netif/ppp/pppos.h

@@ -39,6 +39,14 @@
 
 #include "ppp.h"
 
+/*
+ * PPPoS interface control block.
+ */
+typedef struct pppos_pcb_s pppos_pcb;
+struct pppos_pcb_s {
+  ppp_pcb *ppp;                /* PPP PCB */
+};
+
 /* Create a new PPPoS session. */
 ppp_pcb *ppp_over_serial_create(struct netif *pppif, sio_fd_t fd,
              ppp_link_status_cb_fn link_status_cb, void *ctx_cb);