10_100_1000 Mbps tri-mode ethernet MAC

When RX FIFO FULL signal goes true, the MAC_rx_Ctrl state machine aborts receiving the frame, as it should.

However, the MAC_rx_FIFO.v logic was changed recently to assert Fifo_full up to 4 words earlier using a new signal called Almost_Full.

This has two drawbacks:

1) FIFO space is wasted. This is particularly troublesome when the minimum FIFO length (32) is used.

2) Almost_full does not appear to beneficially prevent a packet from being lost since its assertion causes an abort.

I recommend removing the Almost_Full logic and using original logic ("Full") instead. This allows the entire FIFO to be utilized.