Al Viro pointed out that since there is only one pipe buffer type to which
new data can be appended, it isn't necessary to have a ->can_merge field in
struct pipe_buf_operations, we can just check for a magic type.
Suggested-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NJann Horn <jannh@google.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>