minor, shift ud_get_aux() and ud_scoket_addr() to unserding.h (away from ud-private.h)

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, adapt unsermon to slightly abridged ud_get_aux() api

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'core/api' into next

* core/api:
  minor, adapt unsermon to slightly abridged ud_get_aux() api
  minor, shift ud_get_aux() and ud_scoket_addr() to unserding.h (away from ud-private.h)