This fixes some issues with the 2021.1 version of the 10 GbE IP. In the
new version, link status is sporadically detected by the Xilinx IP when
nothing is connected to the port. Also, when the SFP is inserted, the
link status goes up and down multiple times. This change fixes this by
adding a counter and only considering it "linked" when the link has
been stable for some amount of time.
Original-commit: 846c7be2e42f1db6d7c7cc0b1128e014f83e3bae