esp32/network_ppp: Make PPP support optional.

PPP is not that commonly used, let it be turned off in the board config to
save space.  It is still on by default.

On an basic ESP32-S3 build, turning off PPP with LWIP still on saves ~35 kB
of codend 4 kB of data.

   text    data     bss     dec     hex filename
1321257  304296 2941433 4566986  45afca before-ppp-off.elf
1285101  299920 2810305 4395326  43113e after-ppp-off.elf
-------------------------------
-36156    -4376     -56

Note that the BSS segment size includes all NOBITS sections in ELF file.
Some of these are aligned to 64kB chunk sized dummy blocks, I think for
alignment to MMU boundaries, and these went down by 1 block each, so 128
kiB of BSS is not really part of the binary size reduction.

Signed-off-by: Trent Piepho <tpiepho@gmail.com>

ports/esp32/modnetwork_globals.h

@@ -7,7 +7,9 @@
 #if MICROPY_PY_NETWORK_LAN
 { MP_ROM_QSTR(MP_QSTR_LAN), MP_ROM_PTR(&esp_network_get_lan_obj) },
 #endif
+#if defined(CONFIG_ESP_NETIF_TCPIP_LWIP) && defined(CONFIG_LWIP_PPP_SUPPORT)
 { MP_ROM_QSTR(MP_QSTR_PPP), MP_ROM_PTR(&esp_network_ppp_make_new_obj) },
+#endif
 { MP_ROM_QSTR(MP_QSTR_phy_mode), MP_ROM_PTR(&esp_network_phy_mode_obj) },
 
 #if MICROPY_PY_NETWORK_WLAN

ports/esp32/network_ppp.c

@@ -43,6 +43,8 @@
 #include "lwip/dns.h"
 #include "netif/ppp/pppapi.h"
 
+#if defined(CONFIG_ESP_NETIF_TCPIP_LWIP) && defined(CONFIG_LWIP_PPP_SUPPORT)
+
 #define PPP_CLOSE_TIMEOUT_MS (4000)
 
 typedef struct _ppp_if_obj_t {
@@ -341,3 +343,5 @@ MP_DEFINE_CONST_OBJ_TYPE(
     MP_TYPE_FLAG_NONE,
     locals_dict, &ppp_if_locals_dict
     );
+
+#endif

ports/esp32/ppp_set_auth.c

@@ -9,7 +9,7 @@
 
 #include "ppp_set_auth.h"
 
-#ifdef CONFIG_ESP_NETIF_TCPIP_LWIP
+#if defined(CONFIG_ESP_NETIF_TCPIP_LWIP) && defined(CONFIG_LWIP_PPP_SUPPORT)
 
 #include "netif/ppp/pppapi.h"