Merge branch 'xfrm: add extack support to some more message types'

Sabrina Dubroca says:

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This is the last part of my extack work for xfrm, adding extack
messages to the last remaining operations: NEWSPDINFO, ALLOCSPI,
MIGRATE, NEWAE, DELSA, EXPIRE.

The first patch does a few clean ups on code that will be changed
later on it the series.
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Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>