ixgbe: use EOPNOTSUPP instead of ENOTSUPP in ixgbe_ptp_feature_enable()

When the requested PTP feature is not supported,
ixgbe_ptp_feature_enable() returns -ENOTSUPP, causing userland programs
to get "Unknown error 524".

Since EOPNOTSUPP should be used when error is propagated to userland,
return -EOPNOTSUPP instead of -ENOTSUPP.

Fixes: 3a6a4eda ("ixgbe: Hardware Timestamping + PTP Hardware Clock (PHC)")
Signed-off-by: Kohei Enju <enjuk@amazon.com>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>