Revert commitid: KtmyJEoS0WWxmlZ5

Revert commitid: KtmyJEoS0WWxmlZ5
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Protect interface queues with read once and mutex.

Reading atomic values need at least read once and writing values
should have a mutex.  This is what mbuf queues already do.  Add
READ_ONCE() to ifq and ifiq macros for len and empty.  Convert
ifq_set_maxlen() to a function that grabs ifq_mtx.

OK mvs@
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ifq_set_maxlen() is called before the ifq_mtx is initalized and this at
least crashes WITNESS kernels on boot.

Reported-by: syzbot+7b218ef53432b5d56d7d@syzkaller.appspotmail.com