bpo-31425: Expose AF_QIPCRTR in socket module (GH-3706)

The AF_QIPCRTR address family was introduced in Linux v4.7.

Co-authored-by: Bjorn Andersson <bjorn.andersson@linaro.org>
diff --git a/Doc/library/socket.rst b/Doc/library/socket.rst
index 32e7c5e..44370fe 100644
--- a/Doc/library/socket.rst
+++ b/Doc/library/socket.rst
@@ -193,6 +193,13 @@
   - *addr* - Optional bytes-like object specifying the hardware physical
     address, whose interpretation depends on the device.
 
+- :const:`AF_QIPCRTR` is a Linux-only socket based interface for communicating
+  with services running on co-processors in Qualcomm platforms. The address
+  family is represented as a ``(node, port)`` tuple where the *node* and *port*
+  are non-negative integers.
+
+  .. versionadded:: 3.7
+
 If you use a hostname in the *host* portion of IPv4/v6 socket address, the
 program may show a nondeterministic behavior, as Python uses the first address
 returned from the DNS resolution.  The socket address will be resolved
@@ -481,6 +488,13 @@
    :const:`HCI_DATA_DIR` are not available for FreeBSD, NetBSD, or
    DragonFlyBSD.
 
+.. data:: AF_QIPCRTR
+
+   Constant for Qualcomm's IPC router protocol, used to communicate with
+   service providing remote processors.
+
+   Availability: Linux >= 4.7.
+
 Functions
 ^^^^^^^^^