Auth: increase size of DNS resolver answer buffer

Auth: increase size of DNS resolver answer buffer

This patchset increases the size of the res_search() answer
buffer from 1024 octets to 4096 octets.   This is not a proper
long term solution but will permit sites with longer response
lists to make use of SRV and AFSDB records.

This patchset only impacts UNIX systems.  Windows uses the
Win32 DNS resolver which dynamically allocates memory based
upon the size of the response.

FIXES 130936

Reviewed-on: http://gerrit.openafs.org/7575
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit 3c16a2b296722f548309b10e6744639608c0861b)

Change-Id: Iac7fc7143ff48bd3eb2d3719902dd4549af25b50
Reviewed-on: http://gerrit.openafs.org/7592
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>