Documentation: networking: switchdev: add missing "and" word

Even though this is clear from the context, it is nice to actually be
grammatically correct.

Fixes: 0f22ad45 ("Documentation: networking: switchdev: clarify device driver behavior")
Reported-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>