Restoring old, correct comment for sk_filter_release, moving it to
where it should actually be, and changing new comment into proper
comment for sk_filter_rcu_free, where it actually makes sense.

The original fix submitted for this on Oct 23 mistakenly documented
the wrong function.
Signed-off-by: NPaul Bonser <misterpib@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>