let pfsync_request_update actually retry when it overfills a packet.

let pfsync_request_update actually retry when it overfills a packet.

a continue in the middle of a do { } while (0) loop is effectively
a break, it doesnt restart the loop.

without the retry, the code leaked update messages which in turn
made pool_destroy in pfsync destroy trip over a kassert cos items
were still out.

found by and fix tested by hrvoje popovski
ok sashan@