datapath: Add owner to file_operations declaration.

datapath: Add owner to file_operations declaration.

It's currently possible for operations on our character device to
be still running when we unload the module.  This will result in
an oops when the executing code is suddenly freed.  The chrdev
code has a way to avoid this by taking a reference on the module
every time the device is opened, which means that we can't be
unloaded as long as there is an open file descriptor and therefore
the possibility of an operation.  However, our file_operations
structure doesn't include an owner member, which prevents this
mechanism from working.  This adds one.

Signed-off-by: Jesse Gross <jesse@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>