generic swap(): introduce global macro swap(a, b)

There have been some local definitions of swap(), it's time to replace
them all with a uniform one.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 file changed