Linux: Fix conversion of whole-file locks

Linux: Fix conversion of whole-file locks

An overflow bug in commit 49b7bbdd3b45df694fadbef48f9ed99d9bfe07b9
caused whole-file locks to be treated as byte-range locks, which fail
to be propagated to other machines.

Fix this by setting l_len = 0 for locks that range to the end of the
file.

FIXES 126561

Change-Id: Ie2dc9d04f33559c73b3b86b64152c549b785f8ad
Signed-off-by: Anders Kaseorg <andersk@mit.edu>
Reviewed-on: http://gerrit.openafs.org/1352
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit d3abbebcb0651c5d2c7a3094270fd4f86bea3c1e)
Reviewed-on: http://gerrit.openafs.org/1372