net/skbuff: fix up kernel-doc placement

There are several skb_* functions where the locked and unlocked
functions are confusingly documented. For several of them, the
kernel-doc for the unlocked version is placed above the locked version,
which to the casual reader makes it seems like the locked version "takes
no locks and you must therefore hold required locks before calling it."

One can see, for example, that this link claims to document
skb_queue_head(), while instead describing __skb_queue_head().

https://www.kernel.org/doc/html/latest/networking/kapi.html#c.skb_queue_head



The correct documentation for skb_queue_head() is also included further
down the page.

This diff tested via:

  $ scripts/kernel-doc -rst include/linux/skbuff.h net/core/skbuff.c

No new warnings were seen, and the output makes a little more sense.

Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>