Fix LwIP PBUF_RAM configuration (#29325)

Missed a case of CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_RAM, as
there are no in-tree builds using this configuration. (This used
CHIP_SYSTEM_CONFIG_PACKETBUFFER_LWIP_PBUF_TYPE before #29208.)

Fixes #29282

src/system/SystemPacketBuffer.h

@@ -123,7 +123,7 @@ class DLL_EXPORT PacketBuffer : private pbuf
     /**
      * The maximum size buffer an application can allocate with no protocol header reserve.
      */
-#if CHIP_SYSTEM_PACKETBUFFER_FROM_LWIP_POOL
+#if CHIP_SYSTEM_CONFIG_USE_LWIP
     static constexpr uint16_t kMaxSizeWithoutReserve = LWIP_MEM_ALIGN_SIZE(PBUF_POOL_BUFSIZE);
 #else
     static constexpr uint16_t kMaxSizeWithoutReserve = CHIP_SYSTEM_CONFIG_PACKETBUFFER_CAPACITY_MAX;