cxgbi_inet6addr_handler() can be called in interrupt context, so use rcu
protected list while finding netdev.  This is observed as a scheduling in
atomic oops when running over ipv6.

Fixes: fc8d0590 ("libcxgbi: Add ipv6 api to driver")
Fixes: 759a0cc5 ("cxgb4i: Add ipv6 code to driver, call into libcxgbi ipv6 api")
Signed-off-by: NAnish Bhatt <anish@chelsio.com>
Signed-off-by: NKaren Xie <kxie@chelsio.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJames Bottomley <JBottomley@Parallels.com>