Autoconf: Use a standard test for socklen_t

Autoconf: Use a standard test for socklen_t

Use the standard AC_CHECK_TYPES mechanism to check for the existence
of socklen_t, and to typedef it as an int if it's not found, rather
than growing our own.

Change-Id: Ib5aeb600750558167f63833dd4a7480dbe312b8a
Reviewed-on: http://gerrit.openafs.org/1972
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>