netlink: specs: support setting prefix-name per attribute

Ethtool's PSE PoDL has a attr nest with different prefixes:

/* Power Sourcing Equipment */
enum {
	ETHTOOL_A_PSE_UNSPEC,
	ETHTOOL_A_PSE_HEADER,			/* nest - _A_HEADER_* */
	ETHTOOL_A_PODL_PSE_ADMIN_STATE,		/* u32 */
	ETHTOOL_A_PODL_PSE_ADMIN_CONTROL,	/* u32 */
	ETHTOOL_A_PODL_PSE_PW_D_STATUS,		/* u32 */

Header has a prefix of ETHTOOL_A_PSE_ and other attrs prefix of
ETHTOOL_A_PODL_PSE_ we can't cover them uniformly.
If PODL was after PSE life would be easy.

Now we either need to add prefixes to attr names which is yucky
or support setting prefix name per attr.
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/netlink/genetlink-c.yaml

@@ -195,6 +195,10 @@ properties:
                     description: Max length for a string or a binary attribute.
                     $ref: '#/$defs/len-or-define'
               sub-type: *attr-type
+              # Start genetlink-c
+              name-prefix:
+                type: string
+              # End genetlink-c
 
       # Make sure name-prefix does not appear in subsets (subsets inherit naming)
       dependencies:

Documentation/netlink/genetlink-legacy.yaml

@@ -226,6 +226,10 @@ properties:
                     description: Max length for a string or a binary attribute.
                     $ref: '#/$defs/len-or-define'
               sub-type: *attr-type
+              # Start genetlink-c
+              name-prefix:
+                type: string
+              # End genetlink-c
               # Start genetlink-legacy
               struct:
                 description: Name of the struct type used for the attribute.

tools/net/ynl/ynl-gen-c.py

@@ -58,8 +58,11 @@ class Type(SpecAttr):
         delattr(self, "enum_name")
 
     def resolve(self):
-        self.enum_name = f"{self.attr_set.name_prefix}{self.name}"
-        self.enum_name = c_upper(self.enum_name)
+        if 'name-prefix' in self.attr:
+            enum_name = f"{self.attr['name-prefix']}{self.name}"
+        else:
+            enum_name = f"{self.attr_set.name_prefix}{self.name}"
+        self.enum_name = c_upper(enum_name)
 
     def is_multi_val(self):
         return None