netlink: setsockopt SOL_NETLINK causes otbr to hang on startup

[jdswensen]

Describe the bug

otbr is hanging on startup.

To Reproduce

1. Git commit id
   • [posix] fix logging of netlink errors #9287
2. IEEE 802.15.4 hardware platform
   • Nordic nRF52840 dongle
3. Build steps
   • Built with Yocto, standard BR setup. I can get the build flags if anyone thinks its related.
4. Network topology
   • None. ot-br-posix is failing to start. 😄

Expected behavior
Ideally, some combination of:

• Handle the error without hanging
• If this is a kernel config thing, guard the behavior around a different #define
  • I think SOL_NETLINK is always defined as 270 even if the protocol is not available
• Document what configuration is required to support the new behavior (if any)

Console/log output

[NOTE]-AGENT---: Thread version: 1.3.0
[NOTE]-AGENT---: Thread interface: wpan0
[NOTE]-AGENT---: Radio URL: spinel+hdlc+uart:///dev/ttyACM0
[NOTE]-ILS-----: Infra link selected: eth0
[INFO]-NCP-----: OpenThread log level changed to 5
49d.17:17:38.797 [I] Platform------: RCP reset: RESET_POWER_ON
49d.17:17:38.799 [I] Platform------: RCP reset: RESET_POWER_ON
49d.17:17:38.800 [I] Platform------: Software reset RCP successfully
49d.17:17:38.807 [I] Platform------: Backbone interface is configured to eth0 (2)
49d.17:17:38.809 [C] Platform------: platformConfigureNetLink() at netif.cpp:2007: Protocol not available

Additional context
The platform I'm running on has a pretty minimal distro and kernel config. I'm guessing I'm missing a library or a kconfig option.

[jdswensen]

Let me know if there are any specific logs or other info you may need. It's 100% reproducible on my end if I have that recent netlink commit included.

[wgtdkp]

        VerifyOrDie(setsockopt(sNetlinkFd, SOL_NETLINK, NETLINK_EXT_ACK, &enable, sizeof(enable)) == 0,
                    OT_EXIT_ERROR_ERRNO);

This line is failing. So it looks like we can compile but some how the feature NETLINK_EXT_ACK is not enabled in your setup.

Let me loose the check to simply log a warning when it fails (We don't really depend on those two options to functioning

[wgtdkp]

@jdswensen Cloud you help check if #9299 fixes your issue?