Add some comments to places where we cast through a void* to get rid of alignment warnings

src/api/netdb.c

@@ -364,6 +364,7 @@ lwip_getaddrinfo(const char *nodename, const char *servname,
     return EAI_MEMORY;
   }
   memset(ai, 0, total_size);
+  /* cast through void* to get rid of alignment warnings */
   sa = (struct sockaddr_storage *)(void*)((u8_t*)ai + sizeof(struct addrinfo));
   if (IP_IS_V6_VAL(addr)) {
 #if LWIP_IPV6

src/core/mem.c

@@ -145,6 +145,7 @@ mem_free(void *rmem)
   LWIP_ASSERT("rmem == MEM_ALIGN(rmem)", (rmem == LWIP_MEM_ALIGN(rmem)));
 
   /* get the original struct memp_malloc_helper */
+  /* cast through void* to get rid of alignment warnings */
   hmem = (struct memp_malloc_helper*)(void*)((u8_t*)rmem - LWIP_MEM_ALIGN_SIZE(sizeof(struct memp_malloc_helper)));
 
   LWIP_ASSERT("hmem != NULL", (hmem != NULL));
@@ -357,6 +358,7 @@ mem_free(void *rmem)
   /* protect the heap from concurrent access */
   LWIP_MEM_FREE_PROTECT();
   /* Get the corresponding struct mem ... */
+  /* cast through void* to get rid of alignment warnings */
   mem = (struct mem *)(void *)((u8_t *)rmem - SIZEOF_STRUCT_MEM);
   /* ... which has to be in a used state ... */
   LWIP_ASSERT("mem_free: mem->used", mem->used);
@@ -423,6 +425,7 @@ mem_trim(void *rmem, mem_size_t newsize)
     return rmem;
   }
   /* Get the corresponding struct mem ... */
+  /* cast through void* to get rid of alignment warnings */
   mem = (struct mem *)(void *)((u8_t *)rmem - SIZEOF_STRUCT_MEM);
   /* ... and its offset pointer */
   ptr = (mem_size_t)((u8_t *)mem - ram);

src/core/tcp_out.c

@@ -1174,6 +1174,7 @@ tcp_output_segment(struct tcp_seg *seg, struct tcp_pcb *pcb, struct netif *netif
 
   /* Add any requested options.  NB MSS option is only set on SYN
      packets, so ignore it here */
+  /* cast through void* to get rid of alignment warnings */
   opts = (u32_t *)(void *)(seg->tcphdr + 1);
   if (seg->flags & TF_SEG_OPTS_MSS) {
     u16_t mss;