net: remove useless pfmemalloc setting

When __alloc_skb() allocates an skb from fast clone cache,
setting pfmemalloc on the clone is not needed.

Clone will be properly initialized later at skb_clone() time,
including pfmemalloc field, as it is included in the
headers_start/headers_end section which is fully copied.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>