net: remove two kmemcheck annotations

__alloc_skb() uses a memset() to clear all the beginning of skb,
including bitfields contained in 'flags1' & 'flags2'.

We dont need any more to use kmemcheck_annotate_bitfield() on these
fields. However, we still need it for the clone part, which is not
cleared.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>