Fix IP csum calculation on 8-bit platforms

Author: cpq

mongoose.c

@@ -4206,7 +4206,7 @@ static void mkpay(struct pkt *pkt, void *p) {
 static uint32_t csumup(uint32_t sum, const void *buf, size_t len) {
   size_t i;
   const uint8_t *p = (const uint8_t *) buf;
-  for (i = 0; i < len; i++) sum += i & 1 ? p[i] : (uint32_t) (p[i] << 8);
+  for (i = 0; i < len; i++) sum += i & 1 ? p[i] : ((uint32_t) p[i]) << 8;
   return sum;
 }
 

src/net_builtin.c

@@ -152,7 +152,7 @@ static void mkpay(struct pkt *pkt, void *p) {
 static uint32_t csumup(uint32_t sum, const void *buf, size_t len) {
   size_t i;
   const uint8_t *p = (const uint8_t *) buf;
-  for (i = 0; i < len; i++) sum += i & 1 ? p[i] : (uint32_t) (p[i] << 8);
+  for (i = 0; i < len; i++) sum += i & 1 ? p[i] : ((uint32_t) p[i]) << 8;
   return sum;
 }