net: amd-xgbe: Fix logic around active and passive cables

SFP+ active and passive cables are copper cables with fixed SFP+ end
connectors. Due to a misinterpretation of this, SFP+ active cables could
end up not being recognized, causing the driver to fail to establish a
connection.

Introduce a new enum in SFP+ cable types, XGBE_SFP_CABLE_FIBER, that is
the default cable type, and handle active and passive cables when they are
specifically detected.

Fixes: abf0a1c2 ("amd-xgbe: Add support for SFP+ modules")
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>