docs: netdev: broaden mailbot to all MAINTAINERS

Reword slightly now that all MAINTAINERS have access to the commands.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>