minor: fixed coding style (lwip style)

src/core/ipv4/ip4.c

@@ -538,7 +538,7 @@ ip4_input(struct pbuf *p, struct netif *inp)
       if (netif == inp) {
         netif = netif->next;
       }
-    } while(netif != NULL);
+    } while (netif != NULL);
   }
 
 #if IP_ACCEPT_LINK_LAYER_ADDRESSING

src/core/ipv4/ip4_addr.c

@@ -305,14 +305,14 @@ ip4addr_ntoa_r(const ip4_addr_t *addr, char *buf, int buflen)
 
   rp = buf;
   ap = (u8_t *)&s_addr;
-  for(n = 0; n < 4; n++) {
+  for (n = 0; n < 4; n++) {
     i = 0;
     do {
       rem = *ap % (u8_t)10;
       *ap /= (u8_t)10;
       inv[i++] = '0' + rem;
-    } while(*ap);
-    while(i--) {
+    } while (*ap);
+    while (i--) {
       if (len++ >= buflen) {
         return NULL;
       }

src/core/ipv4/ip_frag.c

@@ -591,7 +591,7 @@ ip4_reass(struct pbuf *p)
     p = ipr->p;
 
     /* chain together the pbufs contained within the reass_data list. */
-    while(r != NULL) {
+    while (r != NULL) {
       iprh = (struct ip_reass_helper*)r->payload;
 
       /* hide the ip header for every succeeding fragment */