tools/net/ynl: Report netlink errors without stacktrace

ynl does not handle NlError exceptions so they get reported like program
failures. Handle the NlError exceptions and report the netlink errors
more cleanly.

Example now:

Netlink error: No such file or directory
nl_len = 44 (28) nl_flags = 0x300 nl_type = 2
	error: -2	extack: {'bad-attr': '.op'}

Example before:

Traceback (most recent call last):
  File "/home/donaldh/net-next/./tools/net/ynl/cli.py", line 81, in <module>
    main()
  File "/home/donaldh/net-next/./tools/net/ynl/cli.py", line 69, in main
    reply = ynl.dump(args.dump, attrs)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/donaldh/net-next/tools/net/ynl/lib/ynl.py", line 906, in dump
    return self._op(method, vals, [], dump=True)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/donaldh/net-next/tools/net/ynl/lib/ynl.py", line 872, in _op
    raise NlError(nl_msg)
lib.ynl.NlError: Netlink error: No such file or directory
nl_len = 44 (28) nl_flags = 0x300 nl_type = 2
	error: -2	extack: {'bad-attr': '.op'}

Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://lore.kernel.org/r/20240306231046.97158-3-donald.hunter@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>