FBSD7: Don't sleep with the glock

FBSD7: Don't sleep with the glock

On FreeBSD 7.X, vinvalbuf() can (will) sleep; this results in a panic
when the kernel is configured with WITNESS and we hold the glock around
it.
Drop the glock in this case.

Reviewed-on: http://gerrit.openafs.org/3551
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit b1cb3607ff66b7fc6201fab2af57761156b1927f)

Change-Id: I3b22c12a20b33ca0e4df5a66c2edfc4167000a1c
Reviewed-on: http://gerrit.openafs.org/3650
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>