vsock_addr: Check for supported flag values

vsock_addr: Check for supported flag values

Check if the provided flags value from the vsock address data structure
includes the supported flags in the corresponding kernel version.

The first byte of the "svm_zero" field is used as "svm_flags", so add
the flags check instead.

Changelog

v3 -> v4

* New patch in v4.

Signed-off-by: Andra Paraschiv <andraprs@amazon.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>