net/mlx5e: Support adaptive RX coalescing

Striving for high message rate and low interrupt rate.

Usage:
        ethtool -C <interface> adaptive-rx on/off

Signed-off-by: Gil Rockah <gilr@mellanox.com>
Signed-off-by: Achiad Shochat <achiad@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
CC: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>