tools: ynl-gen: fix nested array counting

The blamed commit introduced the concept of split attribute
counting, and later allocating an array to hold them, however
TypeArrayNest wasn't updated to use the new counting variable.

Abbreviated example from tools/net/ynl/generated/nl80211-user.c:
nl80211_if_combination_attributes_parse(...):
  unsigned int n_limits = 0;
  [...]
  ynl_attr_for_each(attr, nlh, yarg->ys->family->hdr_len)
	if (type == NL80211_IFACE_COMB_LIMITS)
		ynl_attr_for_each_nested(attr2, attr)
			dst->_count.limits++;
  if (n_limits) {
	dst->_count.limits = n_limits;
	/* allocate and parse attributes */
  }

In the above example n_limits is guaranteed to always be 0,
hence the conditional is unsatisfiable and is optimized out.

This patch changes the attribute counting to use n_limits++ in the
attribute counting loop in the above example.

Fixes: 58da455 ("tools: ynl-gen: improve unwind on parsing errors")
Signed-off-by: Asbjørn Sloth Tønnesen <ast@fiberby.net>
Link: https://patch.msgid.link/20250902160001.760953-1-ast@fiberby.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: Asbjørn Sloth Tønnesen

tools/net/ynl/pyynl/ynl_gen_c.py

@@ -830,7 +830,7 @@ def _attr_get(self, ri, var):
                      'ynl_attr_for_each_nested(attr2, attr) {',
                      '\tif (ynl_attr_validate(yarg, attr2))',
                      '\t\treturn YNL_PARSE_CB_ERROR;',
-                     f'\t{var}->_count.{self.c_name}++;',
+                     f'\tn_{self.c_name}++;',
                      '}']
         return get_lines, None, local_vars