net: skbuff: push nf_trace down the bitfield

nf_trace is a debug feature, AFAIU, and yet it sits oddly
high in the sk_buff bitfield. Move it down, pushing up
dst_pending_confirm and inner_protocol_type.

Next change will make nf_trace optional (under Kconfig)
and all optional fields should be placed after 2b fields
to avoid 2b fields straddling bytes.

dst_pending_confirm is L3, so it makes sense next to ignore_df.
inner_protocol_type goes up just to keep the balance.

Acked-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>