MFC: r285215

remove _NORMAL flag which isn't suppose to be used w/ _alloc_ctx...

MFC: r285289

address an issue where consumers, like IPsec, can reuse the same
session in multiple threads w/o locking.. There was a single fpu
context shared per session, if multiple threads were using the session,
and both migrated away, they could corrupt each other's fpu context...

MFC: r285297

upon further examination, it turns out that _unregister_all already
provides the guarantee that no threads will be in the _newsession code..

MFC: r298332

aesni(4): Initialize error before use [1]

Reported by: Coverity [1]
CID: 1331554 [1]