netlink: introduce type-checking attribute iteration

There are, especially with multi-attr arrays, many cases
of needing to iterate all attributes of a specific type
in a netlink message or a nested attribute. Add specific
macros to support that case.

Also convert many instances using this spatch:

@@
iterator nla_for_each_attr;
iterator name nla_for_each_attr_type;
identifier nla;
expression head, len, rem;
expression ATTR;
type T;
identifier x;
@@
-nla_for_each_attr(nla, head, len, rem)
+nla_for_each_attr_type(nla, ATTR, head, len, rem)
{
<... T x; ...>
-if (nla_type(nla) == ATTR) {
...
-}
}

@@
identifier nla;
iterator nla_for_each_nested;
iterator name nla_for_each_nested_type;
expression attr, rem;
expression ATTR;
type T;
identifier x;
@@
-nla_for_each_nested(nla, attr, rem)
+nla_for_each_nested_type(nla, ATTR, attr, rem)
{
<... T x; ...>
-if (nla_type(nla) == ATTR) {
...
-}
}

@@
iterator nla_for_each_attr;
iterator name nla_for_each_attr_type;
identifier nla;
expression head, len, rem;
expression ATTR;
type T;
identifier x;
@@
-nla_for_each_attr(nla, head, len, rem)
+nla_for_each_attr_type(nla, ATTR, head, len, rem)
{
<... T x; ...>
-if (nla_type(nla) != ATTR) continue;
...
}

@@
identifier nla;
iterator nla_for_each_nested;
iterator name nla_for_each_nested_type;
expression attr, rem;
expression ATTR;
type T;
identifier x;
@@
-nla_for_each_nested(nla, attr, rem)
+nla_for_each_nested_type(nla, ATTR, attr, rem)
{
<... T x; ...>
-if (nla_type(nla) != ATTR) continue;
...
}

Although I had to undo one bad change this made, and
I also adjusted some other code for whitespace and to
use direct variable initialization now.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Link: https://lore.kernel.org/r/20240328203144.b5a6c895fb80.I1869b44767379f204998ff44dd239803f39c23e0@changeid
Signed-off-by: Jakub Kicinski <kuba@kernel.org>