udp: fix gso_segs calculations

udp: fix gso_segs calculations

Commit 9f1ba8f5a67f ("udp: Record gso_segs when supporting UDP segmentation offload")
added gso_segs calculation, but incorrectly got sizeof() the pointer and
not the underlying data type. In addition let's fix the v6 case.

Fixes: a388728846a0 ("udp: generate gso with UDP_SEGMENT")
Fixes: 9f1ba8f5a67f ("udp: Record gso_segs when supporting UDP segmentation offload")
Signed-off-by: Josh Hunt <johunt@akamai.com>
Reviewed-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>