net/mlx5e: Introducing new statistics rwlock

Introduce a new read/write lock that will protect statistics gathering from
netdev channels configuration changes.
e.g. when channels are being replaced (increase/decrease number of rings)
prevent statistic gathering (ndo_get_stats64) to read the statistics of
in-active channels (channels that are being closed).

Plus update channels software statistics on the fly when calling
ndo_get_stats64, and remove it from stats periodic work.

Fixes: 9218b44d ("net/mlx5e: Statistics handling refactoring")
Signed-off-by: Shalom Lagziel <shaloml@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>