mlxsw: spectrum_acl_flex_keys: Add 'ipv4_5b' flex key

The previous patch replaced the key block 'ipv4_4' with 'ipv4_5'. The
corresponding block for Spectrum-4 is 'ipv4_4b'. To be consistent, replace
key block 'ipv4_4b' with 'ipv4_5b'.

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