parallelize ifnet.if_addrhead

["Sepherosa Ziehau" <sepherosa@xxxxxxxxx>]

Hi,

Following patch parallelizes ifnet.if_addrhead accessing
Change ifnet.if_addrhead is serialized by netisr0

Please review it:
http://leaf.dragonflybsd.org/~sephe/ifaddr.diff5

I have run this patch on all of my boxes for ~one month, so it should
be safe to test, if your box is not two miles away from you :)

Best Regards,
sephe

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