Fix delays printing to lpd when reserved ports are exhausted

[bmasonrh]

cups_rresvport() doesn't reserve ports less than 512; however, lpd_queue() continues decrementing the port number to 0. This leads to delays of ~511 seconds once all ports between 512-1023 are exhausted. Even when ports become available, lpd_queue() still tries calling cups_rresvport() with port numbers less than 512, waiting one second between each call.

[zdohnal]

LGTM - port range for old BSD resvport() is 512-1023, so we should reassign lport to the highest value again once we got under the lowest limit to prevent delays.