net: ensure that unix sockets have both split and into_split (#2687)

The documentation build failed with errors such as

error: `[read]` public documentation for `take` links to a private item
    --> tokio/src/io/util/async_read_ext.rs:1078:9
     |
1078 | /         /// Creates an adaptor which reads at most `limit` bytes from it.
1079 | |         ///
1080 | |         /// This function returns a new instance of `AsyncRead` which will read
1081 | |         /// at most `limit` bytes, after which it will always return EOF
...    |
1103 | |         /// }
1104 | |         /// ```
     | |_______________^
     |
note: the lint level is defined here
    --> tokio/src/lib.rs:13:9
     |
13   | #![deny(intra_doc_link_resolution_failure)]
     |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
     = note: the link appears in this line:

             bytes read and future calls to [`read()`][read] may succeed.

1 files changed, 8 insertions, 0 deletions

diff --git a/tokio/src/net/unix/datagram/mod.rs b/tokio/src/net/unix/datagram/mod.rs
new file mode 100644
index 00000000..f484ae34
--- /dev/null
+++ b/tokio/src/net/unix/datagram/mod.rs
@@ -0,0 +1,8 @@
+//! Unix datagram types.
+
+pub(crate) mod socket;
+pub(crate) mod split;
+pub(crate) mod split_owned;
+
+pub use split::{RecvHalf, SendHalf};
+pub use split_owned::{OwnedRecvHalf, OwnedSendHalf, ReuniteError};