Add support for devmem TX in ncdevmem.

This is a combination of the ncdevmem from the devmem TCP series RFCv1
which included the TX path, and work by Stan to include the netlink API
and refactored on top of his generic memory_provider support.

Signed-off-by: Mina Almasry <redacted>
Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>

---

v4:
- Add TX test to devmem.py (Paolo).

v3:
- Update ncdevmem docs to run validation with RX-only and RX-with-TX.
- Fix build warnings (Stan).
- Make the validation expect new lines in the pattern so we can have the
  TX path behave like netcat (Stan).
- Change ret to errno in error() calls (Stan).
- Handle the case where client_ip is not provided (Stan).
- Don't assume mid is <= 2000 (Stan).

v2:
- make errors a static variable so that we catch instances where there
  are less than 20 errors across different buffers.
- Fix the issue where the seed is reset to 0 instead of its starting
  value 1.
- Use 1000ULL instead of 1000 to guard against overflow (Willem).
- Do not set POLLERR (Willem).
- Update the test to use the new interface where iov_base is the
  dmabuf_offset.
- Update the test to send 2 iov instead of 1, so we get some test
  coverage over sending multiple iovs at once.
- Print the ifindex the test is using, useful for debugging issues where
  maybe the test may fail because the ifindex of the socket is different
  from the dmabuf binding.

---
 .../selftests/drivers/net/hw/devmem.py        |  28 +-
 .../selftests/drivers/net/hw/ncdevmem.c       | 300 +++++++++++++++++-
 2 files changed, 312 insertions(+), 16 deletions(-)

diff --git a/tools/testing/selftests/drivers/net/hw/devmem.py b/tools/testing/selftests/drivers/net/hw/devmem.py
index 1223f0f5c10c..3d4f7fc5e63f 100755
--- a/tools/testing/selftests/drivers/net/hw/devmem.py
+++ b/tools/testing/selftests/drivers/net/hw/devmem.py

@@ -1,6 +1,7 @@
 #!/usr/bin/env python3
 # SPDX-License-Identifier: GPL-2.0
 
+from os import path
 from lib.py import ksft_run, ksft_exit
 from lib.py import ksft_eq, KsftSkipEx
 from lib.py import NetDrvEpEnv

@@ -10,8 +11,7 @@ from lib.py import ksft_disruptive
 
 def require_devmem(cfg):
     if not hasattr(cfg, "_devmem_probed"):
-        port = rand_port()
-        probe_command = f"./ncdevmem -f {cfg.ifname}"
+        probe_command = f"{cfg.bin_local} -f {cfg.ifname}"
         cfg._devmem_supported = cmd(probe_command, fail=False, shell=True).ret == 0
         cfg._devmem_probed = True
 

@@ -25,18 +25,36 @@ def check_rx(cfg) -> None:
     require_devmem(cfg)
 
     port = rand_port()
-    listen_cmd = f"./ncdevmem -l -f {cfg.ifname} -s {cfg.v6} -p {port}"
+    listen_cmd = f"{cfg.bin_local} -l -f {cfg.ifname} -s {cfg.v6} -p {port}"
 
     with bkg(listen_cmd) as socat:
         wait_port_listen(port)
-        cmd(f"echo -e \"hello\\nworld\"| socat -u - TCP6:[{cfg.v6}]:{port}", host=cfg.remote, shell=True)
+        cmd(f"echo -e \"hello\\nworld\"| socat -u - TCP6:{cfg.v6}:{port},bind={cfg.remote_v6}:{port}", host=cfg.remote, shell=True)