lustre: Account for changelog_ext_rec in CR_MAXSIZE

CR_MAXSIZE needs to account for an llog_changelog_rec that actually
contains a changelog_ext_rec structure rather than a changelog_rec.
With out doing so, a file size approaching the Linux kernel NAME_MAX
length that is renamed to a size also close to, or at, NAME_MAX will
exceed CR_MAXSIZE and trip an assertion.

Signed-off-by: Christopher J. Morrone <morrone2@llnl.gov>
Reviewed-on: http://review.whamcloud.com/6993
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3587


Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>