MINOR: stats: uniformize the calling convention of the dump functions

MINOR: stats: uniformize the calling convention of the dump functions

Some functions used to take flags + appctx with flags==appctx.flags,
others neither, others just one of them. Some functions used to have
the flags before the object being dumped (server) while others had
it after (listener). This patch aims at cleaning this up a little bit
by following this principle:
  - low-level functions which do not need the appctx take flags only
  - medium-level functions which already use the appctx for other
    reasons do not keep the flags
  - top-level functions which already have the stream-int don't need
    the flags nor the appctx.