crypto: api - Add crypto_tfm_get

[ Upstream commit ae131f49 ]

Add a crypto_tfm_get interface to allow tfm objects to be shared.
They can still be freed in the usual way.

This should only be done with tfm objects with no keys.  You must
also not modify the tfm flags in any way once it becomes shared.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Stable-dep-of: 1465036b ("llc: Improve setsockopt() handling of malformed user input")
Signed-off-by: Sasha Levin <sashal@kernel.org>