bnx2x: 57840 non-external loopback test fail on 1G

when 1G-optic module was plugged in, internal loopback test failed because the
driver used to check the optic module (with no need), and for 1G optic module,
the link speed was forced down to 1G, while the XMAC (10G MAC) was enabled.
This patch avoid accessing optic module in case internal loopback was selected,
and update the link speed in case 1G optic module was detected during init
stage.

Signed-off-by: Yaniv Rosner <yanivr@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>