UPSTREAM: net: core: reject skb_copy(_expand) for fraglist GSO skbs

SKB_GSO_FRAGLIST skbs must not be linearized, otherwise they become
invalid. Return NULL if such an skb is passed to skb_copy or
skb_copy_expand, in order to prevent a crash on a potential later
call to skb_gso_segment.

Bug: 254441685
Fixes: 3a1296a38d0c ("net: Support GRO/GSO fraglist chaining.")
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit d091e579b864fa790dd6a0cd537a22c383126681)
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: I0835421359096bd9566a09037d43db84f371dcb1