af_unix: Add unix_stream_proto for sockmap

af_unix: Add unix_stream_proto for sockmap

Previously, sockmap for AF_UNIX protocol only supports
dgram type. This patch add unix stream type support, which
is similar to unix_dgram_proto. To support sockmap, dgram
and stream cannot share the same unix_proto anymore, because
they have different implementations, such as unhash for stream
type (which will remove closed or disconnected sockets from the map),
so rename unix_proto to unix_dgram_proto and add a new
unix_stream_proto.

Also implement stream related sockmap functions.
And add dgram key words to those dgram specific functions.

Signed-off-by: Jiang Wang <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Reviewed-by: Cong Wang <[email protected]>
Acked-by: Jakub Sitnicki <[email protected]>
Acked-by: John Fastabend <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]