Revert "blackhole_netdev: fix syzkaller reported issue"

This reverts commit b0818f80

.

Started seeing weird behavior after this patch especially in
the IPv6 code path. Haven't root caused it, but since this was
applied to net branch, taking a precautionary measure to revert
it and look / analyze those failures

Revert this now and I'll send a better fix after analysing / fixing
the weirdness observed.

CC: Eric Dumazet <edumazet@google.com>
CC: Wei Wang <weiwan@google.com>
CC: David S. Miller <davem@davemloft.net>
Signed-off-by: Mahesh Bandewar <maheshb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>