Fix incorrect preprocessor usage of LwIP PBUF_POOL (project-chip#29232)

Configuration allowed specifying an LwIP `pbuf_type` value for
`System::PacketBuffer` allocations, and code tested this configuration
in preprocessor conditions; however, the LwIP names are enum constants,
not preprocessor defintions.

This change replaces the configuration macro with a new one selecting
between `PBUF_POOL` and `PBUF_RAM`. (From PR#14257 that introduced the
configuration, it does not appear that other options were ever used.)

Fixes project-chip#29208

src/system/SystemConfig.h

@@ -359,15 +359,21 @@
 #endif /* CHIP_SYSTEM_CONFIG_PACKETBUFFER_POOL_SIZE */
 
 /**
- *  @def CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_TYPE
+ *  @def CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_RAM
  *
  *  @brief
- *      LwIP @pbuf_type for System::PacketBuffer allocations.
+ *      In LwIP builds, this selects whether to use LwIP @pbuf_type @PBUF_RAM (1)
+ *      or @PBUF_POOL (0) for System::PacketBuffer allocations.
  *
  *      Note that this does not affect allocations by LwIP itself, e.g. the normal receive path.
  */
-#ifndef CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_TYPE
-#define CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_TYPE PBUF_POOL
+#ifndef CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_RAM
+#define CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_RAM 0
+#endif /* CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_RAM */
+
+// Catch configurations attempting to use the former method (see issue #29208).
+#ifdef CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_TYPE
+#error "See CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_RAM"
 #endif /* CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_TYPE */
 
 /**

src/system/SystemPacketBuffer.cpp

@@ -501,7 +501,7 @@ PacketBufferHandle PacketBufferHandle::New(size_t aAvailableSize, uint16_t aRese
 #if CHIP_SYSTEM_CONFIG_USE_LWIP
 
     lPacket = static_cast<PacketBuffer *>(
-        pbuf_alloc(PBUF_RAW, static_cast<uint16_t>(lAllocSize), CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_TYPE));
+        pbuf_alloc(PBUF_RAW, static_cast<uint16_t>(lAllocSize), CHIP_SYSTEM_PACKETBUFFER_LWIP_PBUF_TYPE));
 
     SYSTEM_STATS_UPDATE_LWIP_PBUF_COUNTS();
 

src/system/SystemPacketBufferInternal.h

@@ -54,12 +54,25 @@
  *
  * True if packet buffers are allocated from an LwIP pool (either standard or custom).
  */
-#if CHIP_SYSTEM_CONFIG_USE_LWIP && (CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_TYPE == PBUF_POOL)
+#if CHIP_SYSTEM_CONFIG_USE_LWIP && !CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_RAM
 #define CHIP_SYSTEM_PACKETBUFFER_FROM_LWIP_POOL 1
 #else
 #define CHIP_SYSTEM_PACKETBUFFER_FROM_LWIP_POOL 0
 #endif
 
+/**
+ * CHIP_SYSTEM_PACKETBUFFER_LWIP_PBUF_TYPE
+ *
+ * LwIP @pbuf_type for System::PacketBuffer allocations.
+ */
+#if CHIP_SYSTEM_CONFIG_USE_LWIP
+#if CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_RAM
+#define CHIP_SYSTEM_PACKETBUFFER_LWIP_PBUF_TYPE PBUF_RAM
+#else
+#define CHIP_SYSTEM_PACKETBUFFER_LWIP_PBUF_TYPE PBUF_POOL
+#endif
+#endif
+
 /**
  * CHIP_SYSTEM_PACKETBUFFER_FROM_LWIP_STANDARD_POOL
  *
@@ -114,3 +127,7 @@
     CHIP_SYSTEM_PACKETBUFFER_FROM_LWIP_POOL
 #error "Inconsistent PacketBuffer LwIP pool configuration"
 #endif
+
+#if (CHIP_SYSTEM_PACKETBUFFER_FROM_LWIP_POOL + CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_RAM) > 1
+#error "Inconsistent PacketBuffer LwIP pbuf_type configuration"
+#endif