r8169: Rx FIFO overflow fixes.

Realtek has specified that the post 8168c gigabit chips and the post
8105e fast ethernet chips recover automatically from a Rx FIFO overflow.
The driver does not need to clear the RxFIFOOver bit of IntrStatus and
it should rather avoid messing it.

The implementation deserves some explanation:
1. events outside of the intr_event bit mask are now ignored. It enforces
   a no-processing policy for the events that either should not be there
   or should be ignored.

2. RxFIFOOver was already ignored in rtl_cfg_infos[RTL_CFG_1] for the
   whole 8168 line of chips with two exceptions:
   - RTL_GIGA_MAC_VER_22 since b5ba6d12
     ("use RxFIFO overflow workaround for 8168c chipset.").
     This one should now be correctly handled.
   - RTL_GIGA_MAC_VER_11 (8168b) which requires a different Rx FIFO
     overflow processing.

   Though it does not conform to Realtek suggestion above, the updated
   driver includes no change for RTL_GIGA_MAC_VER_12 and RTL_GIGA_MAC_VER_17.
   Both are 8168b. RTL_GIGA_MAC_VER_12 is common and a bit old so I'd rather
   wait for experimental evidence that the change suggested by Realtek really
   helps or does not hurt in unexpected ways.

   Removed case statements in rtl8169_interrupt are only 8168 relevant.

3. RxFIFOOver is masked for post 8105e 810x chips, namely the sole 8105e
   (RTL_GIGA_MAC_VER_30) itself.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Cc: hayeswang <hayeswang@realtek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>