net: core: Revert patch 399525c5dfd910909d62f935d27049fff9c1df58

It just made things worse. With that patch MPLS flag couldn't be unset.
net: Added function for setting dev flags with short

When net_device flags were set with unsigned short, upper 16 flag bits were ignored.
So, when setting net_device flags with unsigned short, copy upper 16 flag bits to the
change flag request.