net: skbuff: fix kernel-doc typos

Correct punctuation and drop an extraneous word.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20231008214121.25940-1-rdunlap@infradead.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>