lpool: use offset to next, avoids pointer alignment requirments

include/lpool.h

@@ -9,7 +9,7 @@ extern "C" {
 
 typedef union LPoolBlock LPoolBlock;
 union LPoolBlock {
-    LPoolBlock *next;       // next free block (when not allocated)
+    uint32_t next;          // offset from start to next free block (when not allocated)
     unsigned char data[0];  // data when allocated
 };
 
@@ -30,8 +30,8 @@ union LPoolBlock {
 typedef struct LPool LPool;
 struct LPool {
     LPoolBlock *free_list;  // free list
-    LPoolBlock *start;      // start of user buffer
-    LPoolBlock *end;        // one past end of user buffer
+    uint8_t *start;         // start of user buffer
+    uint8_t *end;           // one past end of user buffer
     uint32_t block_size;    // aligned size of each block
     uint32_t capacity;      // number of blocks
     uint32_t align;         // alignment