During FUSE_SETLK, the owner field should uniquely identify the calling
process. The fusefs module now sets it to the process's pid.
Previously, it expected the calling process to set it directly, which
libfuse also apparently expects the owner field to be set during
FUSE_GETLK, though I'm not sure why.
Reported by: Agata <email@example.com>
MFC after: 2 weeks