net/core: remove duplicate statements by do-while loop

Remove duplicate statements by using do-while loop instead of while loop.

- A;
- while (e) {
+ do {
	A;
- }
+ } while (e);

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>