mlxsw: spectrum_ethtool: Add an external speed to PTYS register

Currently, only external bits are added to the PTYS register, whereas
there is one external bit that is wrongly marked as internal, and so was
recently removed from the register.

Add that bit to the PTYS register again, as this bit is no longer
internal.

Its removal resulted in '100000baseLR4_ER4/Full' link mode no longer
being supported, causing a regression on some setups.

Fixes: 5bf01b57 ("mlxsw: spectrum_ethtool: Remove internal speeds from PTYS register")
Signed-off-by: Danielle Ratson <danieller@nvidia.com>
Reported-by: Eddie Shklaer <eddies@nvidia.com>
Tested-by: Eddie Shklaer <eddies@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>