On a PSP, a PDP socket created on port 0 gets a free port between
0x1000 and 0x7FFF (pspautotests net/adhoc/limits). The host picked
one instead, usually 0x8000 or above once the port offset was taken
off. Pick it the way PtpOpen already does for PTP, and try another if
the host port is taken. Port 0 still doesn't become the fixed port the
offset alone would give (Phantasy Star Portable 2).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>