collectors: Use closesocket() to close sockets.

We should use closesocket() while closing sockets so that
closing sockets work fine on both POSIX and Windows.
(In POSIX, we #define closesocket close)

Without this change, sflow unit tests would cause ovs-vswitchd
to crash in Windows.

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>

ofproto/collectors.c

@@ -95,7 +95,7 @@ collectors_destroy(struct collectors *c)
         size_t i;
 
         for (i = 0; i < c->n_fds; i++) {
-            close(c->fds[i]);
+            closesocket(c->fds[i]);
         }
         free(c->fds);
         free(c);