tools: pynl: make flags argument optional for do()

Commit 1768d8a7 ("tools/net/ynl: Add support for create flags")
added support for setting legacy netlink CRUD flags on netlink
messages (NLM_F_REPLACE, _EXCL, _CREATE etc.).

Most of genetlink won't need these, don't force callers to pass
in an empty argument to each do() call.
Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://lore.kernel.org/r/20231202211005.341613-1-kuba@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/net/ynl/lib/ynl.py

@@ -705,7 +705,7 @@ class YnlFamily(SpecFamily):
 
       return op['do']['request']['attributes'].copy()
 
-    def _op(self, method, vals, flags, dump=False):
+    def _op(self, method, vals, flags=None, dump=False):
         op = self.ops[method]
 
         nl_flags = Netlink.NLM_F_REQUEST | Netlink.NLM_F_ACK
@@ -769,7 +769,7 @@ class YnlFamily(SpecFamily):
             return rsp[0]
         return rsp
 
-    def do(self, method, vals, flags):
+    def do(self, method, vals, flags=None):
         return self._op(method, vals, flags)
 
     def dump(self, method, vals):