spec: kernel requirements on EL6

kernel-2.6.32-465.el6 solves a few NFSv4 issues.
Since VDSM supports NFSv4, it should require this kernel version to
ensure it avoids those bugs.

Note that this fix is not relevant for EL7 and modern Fedora builds,
which use kernel versions from the 3.x generation.

Change-Id: I93bbde6e808e319baa5fda37d8630f1ffa9f5a03
Bug-Url: https://bugzilla.redhat.com/1075123
Signed-off-by: Allon Mureinik <amureini@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/36191
Reviewed-by: Dan Kenigsberg <danken@redhat.com>