ipv4: fib: Send deletion notification with actual FIB alias type

When a FIB alias is removed, a notification is sent using the type
passed from user space - can be RTN_UNSPEC - instead of the actual type
of the removed alias. This is problematic for listeners of the FIB
notification chain, as several FIB aliases can exist with matching
parameters, but the type.

Solve this by passing the actual type of the removed FIB alias.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
CC: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>