ix(4): Remove workaround for 2.5/5G speeds on E610

The problem observed on X550 adapters with 2.5 and 5 Gbps speeds
negotiation on some switches is not affecting E610 adapters.
Remove workaround, which omitted those speeds in the list
of initially advertised speeds and advertise all speeds
supported by adapter.

Signed-off-by: Krzysztof Galazka <krzysztof.galazka@intel.com>

Reviewed by: kbowling
Tested by: Mateusz Moga <mateusz.moga@intel.com>
MFC after: 1 week
Sponsored by: Intel Corporation
Differential Revision: https://reviews.freebsd.org/D57339