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

Change-Id: I8434e128fb5918839c216209851b37a17cf94065
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>