[GFS2] increase default lock limit

Increase the number of locks at which point the dlm begins asking gfs to
reduce its lock usage.  The default value is largely arbitrary, but the
current value of 50,000 ends up limiting performance unnecessarily for too
many users.

Signed-off-by: David Teigland <teigland@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>