Fix net_send_all()

On partial writes, the final result was the number of bytes written by
the last send() rather than the total.

app/src/util/net.c

@@ -99,16 +99,18 @@ net_send(socket_t socket, const void *buf, size_t len) {
 
 ssize_t
 net_send_all(socket_t socket, const void *buf, size_t len) {
+    size_t copied = 0;
     ssize_t w = 0;
     while (len > 0) {
         w = send(socket, buf, len, 0);
         if (w == -1) {
-            return -1;
+            return copied ? (ssize_t) copied : -1;
         }
         len -= w;
         buf = (char *) buf + w;
+        copied += w;
     }
-    return w;
+    return copied;
 }
 
 bool