drop_monitor: Add module alias to enable automatic module loading

Now that we have module alias macros for generic netlink families, lets use
those to mark modules with the appropriate family names for loading

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: Eric Dumazet <eric.dumazet@gmail.com>
CC: David Miller <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>