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.

arch/mips/bits/stat.h

@@ -1,8 +1,7 @@
 /* copied from kernel definition, but with padding replaced
  * by the corresponding correctly-sized userspace types. */
 
-struct stat
-{
+struct stat {
 	dev_t st_dev;
 	long __st_padding1[2];
 	ino_t st_ino;