Support for ALG_SET_KEY_BY_KEY_SERIAL for af_alg sockets

[rzimmerman]

For Linux platforms, support for using the Kernel keyring as a key source for af_alg calls to the crypto API was added in v6.1:
https://lkml.org/lkml/2022/10/4/1014
https://elixir.bootlin.com/linux/latest/source/include/uapi/linux/if_alg.h#L55
https://docs.kernel.org/crypto/userspace-if.html#setsockopt-interface

which added a ALG_SET_KEY_BY_KEY_SERIAL option. The option takes a single argument, a keyring identifier.

It would be great to support this directly.