make brace placement in public header struct definitions consistent

placing the opening brace on the same line as the struct keyword/tag
is the style I prefer and seems to be the prevailing practice in more
recent additions.

these changes were generated by the command:

find include/ arch/*/bits -name '*.h' \
-exec sed -i '/^struct [^;{]*$/{N;s/\n/ /;}' {} +

and subsequently checked by hand to ensure that the regex did not pick
up any false positives.

include/net/if.h

@@ -9,8 +9,7 @@ extern "C" {
 
 #define IF_NAMESIZE 16
 
-struct if_nameindex
-{
+struct if_nameindex {
 	unsigned int if_index;
 	char *if_name;
 };