Fix delays in printing to lpd when reserved ports are exhausted (Issue #741)

Fix delays in printing to lpd when reserved ports are exhausted (Issue #741)

We use our internal implementation for BSD resvport() by default in LPD backend, which should act on port ranges 512 - 1023, however we didn't go back to the highest port number once we got under the lowest port number. This caused a delay 511s long until  `lpd_queue()` got the port number to 0, which triggered the assignment of the highest port number.

The highest port number is assigned right after we cross the lowest port number, which eliminates this kind of delay.

PR by Bryan Mason from Red Hat