ice: Ignore EMODE return for opcode 0x0605

When link is owned by manageability, the driver is not allowed to fiddle
with link. FW returns ICE_AQ_RC_EMODE if the driver attempts to do so.
This patch adds a new function ice_set_link which abstracts the call to
ice_aq_set_link_restart_an and provides a clean way to turn on/off link.

While making this change, I also spotted that an int variable was being
used to hold both an ice_status return code and the Linux errno return
code. This pattern more often than not results in the driver inadvertently
returning ice_status back to kernel which is a major boo-boo. Clean it up.

Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@intel.com>
Tested-by: Tony Brelinski <tonyx.brelinski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>