LU-15366 nrs: increase maximum rate for tbf rule

LU-15366 nrs: increase maximum rate for tbf rule

The maximum rpc rate for a tbf rule is 65535. This value could be
problematic for cluster with a large number of clients.

This patch uniformizes the usage of __u64 to store a rpc rate.
And changes the maximum rate for a tbf rule to 1000000 (1 rpc/us)

Signed-off-by: Etienne AUJAMES <eaujames@ddn.com>
Change-Id: I91fd416b9d91bbb5d5674c66ec8ceb0d77a9f7e0
Reviewed-on: https://review.whamcloud.com/45838
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Yingjin Qian <qian@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>