staging: lustre: Allocate the correct number of rtr buffers

This patch ensures that the correct number of router buffers are
allocated.  It keeps a count that keeps track of the number of
buffers allocated.  Another count keeps the number of buffers
requested. The number of buffers allocated is set when creating
new buffers and reduced when buffers are freed.

The number of requested buffer is set when the buffers are
allocated and is checked when credits are returned to determine
whether the buffer should be freed or kept.

In lnet_rtrpool_adjust_bufs() grab lnet_net_lock() before using
rbp_nbuffers to ensure that it doesn't change by
lnet_return_rx_credits_locked() during the process of allocating
new buffers.  All other access to rbp_nbuffers is already being
protected by lnet_net_lock().

This avoids the case where we allocate less than the desired
number of buffers.

Signed-off-by: Amir Shehata <amir.shehata@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-6122
Reviewed-on: http://review.whamcloud.com/13519


Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Doug Oucharek <doug.s.oucharek@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>