Most of this is extracted from 90017acc ("sctp: Add GSO support"),
with some extra text about GSO_BY_FRAGS and the need to check for it.

Cc: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: NDaniel Axtens <dja@axtens.net>
Acked-by: NMarcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>