Fall back to unsigned int, not int, for socklen_t.
It's a coin toss which of these is a better default assumption.
However, of the machines we have in the buildfarm, the only ones
relying on the fallback socklen_t definition are ancient HPUX,
and on that platform unsigned int is the right choice. Minor
tweak to
ee3a1a5b6.
Discussion: https://postgr.es/m/
1440792.
1636558888@sss.pgh.pa.us