MEDIUM: splice: Don't consider EINVAL to be a fatal error

MEDIUM: splice: Don't consider EINVAL to be a fatal error

Don't consider that EINVAL is a fatal error, when calling splice().
When doing splicing from a kTLS socket, splice() will set errno to
EINVAL if the next record to be read is not an application data record.
This is not a fatal error, it just means we have to use recvmsg() to
read it, and potentially we can then resume using splicing.
It is unfortunate that EINVAL was used for that case, but we should
never get any other case of receiving EINVAL from splice(), so it should
be safe to treat it as non-fatal.