ixgbevf: Rename MSGTYPE to SUCCESS and FAILURE

There is name similarity within IXGBE_VT_MSGTYPE_ACK and
PFMAILBOX.ACK / VFMAILBOX.ACK. MSGTYPE macros are renamed to SUCCESS and
FAILURE because they are not specified in datasheet and now will be
easily distinguishable.

Signed-off-by: Radoslaw Tyl <radoslawx.tyl@intel.com>
Tested-by: Tony Brelinski <tony.brelinski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>