mlxsw: cmd: Increase 'config_profile.flood_mode' length

Currently, the length of 'config_profile.flood_mode' is defined as 2
bits, while the correct length is 3 bits.

As preparation for unified bridge model, which will use the whole field
length, fix it and increase the field to the correct size.

Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>