The driver can present all SW stats even when the state not opened.
Fixed get strings, count and stats to support it.

In addition, fix tc2txq to hold a static mapping which doesn't depend on
the amount of open channels, and cannot have the same value on two
different cells  while moving between configurations.
Example:
- OOB 16 channels
- Change to 2 channels, 8 TCs
- tc2txq[15][0] == tc2txq[1][7] == 15
This will cause multiple appearances of the same TX index in statistics
output.

Fixes: 76c3810bade3 ("net/mlx5e: Avoid reset netdev stats on configuration changes")
Signed-off-by: Eran Ben Elisha <eranbe@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>