kabi: add early_demux_handler and early_demux back to fix kabi broken in struct net_protocol and inet6_protocol

Offering: HULK
hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6D0ZE

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Add early_demux_handler and early_demux back to fix kabi broken in
struct net_protocol and inet6_protocol.
Signed-off-by: NWang Yufen <wangyufen@huawei.com>
Reviewed-by: NLiu Jian <liujian56@huawei.com>
Signed-off-by: NJialin Zhang <zhangjialin11@huawei.com>