pgsql: Get rid of unportable use of socklen_t --- we have a configure

Log Message:
-----------
Get rid of unportable use of socklen_t --- we have a configure test
for that, so use it.

Modified Files:
--------------
pgsql/src/backend/libpq:
auth.c (r1.192 -> r1.193)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/auth.c?r1=1.192&r2=1.193)