fs: dlm: change posix lock sigint handling

This patch changes the handling of a plock operation that was interrupted
while waiting for a user space reply from dlm_controld.  (This is not
the lock blocking state, i.e. locks_lock_file_wait().)

Currently, when an op is interrupted while waiting on user space, the
op is removed.  When the user space result later arrives, a kernel
message is loggged: "dev_write no op...".  This can be seen from a test
such as "stress-ng --fcntl 100" and interrupting it with ctrl-c.

Now, leave the op in place when interrupted and remove it when the
result arrives (the result will be ignored.)  With this change, the
logged message is not expected to appear, and would indicate a bug.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>