LinuxKPI: sk_buff: implement skb_queue_splice_tail_init()

Implement skb_queue_splice_tail_init() and SKB_DATA_ALIGN() as
needed by the mt76 wireless driver.

Sponsord by: The FreeBD Foundation
Reviewed by: emaste
Differential Revision: https://reviews.freebsd.org/D44590

(cherry picked from commit 3d3ec17825a124f0119d76c4d2523d73012fa226)