tools: ynl: add more info to KeyErrors on missing attrs

When developing specs its useful to know which attr space
YNL was trying to find an attribute in on key error.

Instead of printing:
 KeyError: 0
add info about the space:
 Exception: Space 'vport' has no attribute with value '0'
Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://lore.kernel.org/r/20230814205627.2914583-4-kuba@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/net/ynl/lib/ynl.py

@@ -395,7 +395,10 @@ class YnlFamily(SpecFamily):
                              self.family.genl_family['mcast'][mcast_name])
 
     def _add_attr(self, space, name, value):
-        attr = self.attr_sets[space][name]
+        try:
+            attr = self.attr_sets[space][name]
+        except KeyError:
+            raise Exception(f"Space '{space}' has no attribute '{name}'")
         nl_type = attr.value
         if attr["type"] == 'nest':
             nl_type |= Netlink.NLA_F_NESTED
@@ -450,7 +453,10 @@ class YnlFamily(SpecFamily):
         attr_space = self.attr_sets[space]
         rsp = dict()
         for attr in attrs:
-            attr_spec = attr_space.attrs_by_val[attr.type]
+            try:
+                attr_spec = attr_space.attrs_by_val[attr.type]
+            except KeyError:
+                raise Exception(f"Space '{space}' has no attribute with value '{attr.type}'")
             if attr_spec["type"] == 'nest':
                 subdict = self._decode(NlAttrs(attr.raw), attr_spec['nested-attributes'])
                 decoded = subdict
@@ -479,7 +485,10 @@ class YnlFamily(SpecFamily):
 
     def _decode_extack_path(self, attrs, attr_set, offset, target):
         for attr in attrs:
-            attr_spec = attr_set.attrs_by_val[attr.type]
+            try:
+                attr_spec = attr_set.attrs_by_val[attr.type]
+            except KeyError:
+                raise Exception(f"Space '{attr_set.name}' has no attribute with value '{attr.type}'")
             if offset > target:
                 break
             if offset == target: