tools: ynl: don't ignore errors in NLMSG_DONE messages

[ Upstream commit a44f2eb106a46f2275a79de54ce0ea63e4f3d8c8 ]

NLMSG_DONE contains an error code, it has to be extracted.
Prior to this change all dumps will end in success,
and in case of failure the result is silently truncated.

Fixes: e4b48ed460 ("tools: ynl: add a completely generic client")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://lore.kernel.org/r/20240420020827.3288615-1-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

tools/net/ynl/lib/ynl.py

@@ -201,6 +201,7 @@ class NlMsg:
             self.done = 1
             extack_off = 20
         elif self.nl_type == Netlink.NLMSG_DONE:
+            self.error = struct.unpack("i", self.raw[0:4])[0]
             self.done = 1
             extack_off = 4