When the user changes prio2buffer mapping while global pause is
enabled, mlx5 driver incorrectly sets all active buffers
(buffer that has at least one priority mapped) to lossy.

Solution:
If global pause is enabled, set all the active buffers to lossless
in prio2buffer command.
Also, add error message when buffer size is not enough to meet
xoff threshold.

Fixes: 0696d608 ("net/mlx5e: Receive buffer configuration")
Signed-off-by: Huy Nguyen <huyn@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>