[NET]: Introduce types for checksums.

New types - for 16bit checksums and "unfolded" 32bit variant.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/types.h

@@ -182,6 +182,8 @@ typedef __u32 __bitwise __be32;
 typedef __u64 __bitwise __le64;
 typedef __u64 __bitwise __be64;
 #endif
+typedef __u16 __bitwise __sum16;
+typedef __u32 __bitwise __wsum;
 
 #ifdef __KERNEL__
 typedef unsigned __bitwise__ gfp_t;