LinuxKPI: skbuff: fix skb_queue_splice_init()

In skb_queue_splice_init() we set a next value and then used that new
value to further update the remaining linking rather than the original
value. Introduce another temporary variable 'n' to hold the original
value and use that.
While here rename q and h to from and to as otherwise it was too
confusing to read.

Also initialize skb->prev and skb->next to point to skb itself if
for nothing else at least to aid debugging.

Reported by: phk (panic in iwl_txq_reclaim)
Sponsored by: The FreeBSD Foundation
MFC after: 3 days