nat: NAT44 ED api fix and improvement

nat: NAT44 ED api fix and improvement

Backward compatibility fix returns erroneous behavior that lets user
add internally unused inside interface for the purpose
of complying with the old add/dump/details API behavior.
Change introduced in https://gerrit.fd.io/r/c/vpp/+/32951 removed
extra inside interface that wasn't required or any how used by the
output feature. This patch also changed outside interface flags to
inside & outside. This fix returns the old behavior by imitating
the old behavior through dummy registratoin data.

Added new API calls nat44_ed_add_del_output_interface
and nat44_ed_output_interface_get/details as a
replacement of old API's. New API introduces
simplified and cleaner way of configuring outside
feature without requirement of config flags.

Type: improvement
Signed-off-by: Filip Varga <fivarga@cisco.com>
Change-Id: I7a170f7325727c04da5e2e3ffbe3f02179531284