fix: dev: Fix port validation rejecting valid port 65535

Three port validation checks use >= UINT16_MAX instead of > UINT16_MAX,
incorrectly rejecting port 65535 as out of range.  Port 65535 is a valid
TCP/UDP port number.  Other port checks in the same file already use the
correct > comparison.

Merge branch 'ondrej/fix-port-validation-rejecting-valid-port-65535' into 'main'

See merge request isc-projects/bind9!11665