Adding support to have priv pointer in swap callback function.

Following the initial change on cmp callback functions [1]
and adding SWAP_WRAPPER macro to identify sort call of sort_r.
Signed-off-by: NJiri Olsa <jolsa@kernel.org>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Reviewed-by: NMasami Hiramatsu <mhiramat@kernel.org>
Link: https://lore.kernel.org/bpf/20220316122419.933957-2-jolsa@kernel.org

[1] 4333fb96 ("media: lib/sort.c: implement sort() variant taking context argument")