AIX 5L has socklen_t, so use it so we avoid some warnings

AIX 4.3.3 has socklen_t too, but

a) I don't know if all 4.3 (e.g., 4.3.0) has it
b) I don't see the warning on 4.3
c) it isn't a possible 64-bit vs. 32-bit problem, so I'm not
   worried about run-time breakage


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@91392 13f79535-47bb-0310-9956-ffa450edef68