r8152: fix the sw rx checksum is unavailable

Fix the hw rx checksum is always enabled, and the user couldn't switch
it to sw rx checksum.

Note that the RTL_VER_01 only support sw rx checksum only. Besides,
the hw rx checksum for RTL_VER_02 is disabled after
commit b9a321b4 ("r8152: Fix broken RX checksums."). Re-enable it.

Signed-off-by: Hayes Wang <hayeswang@realtek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>