nat: fix update of outside fibs (output-feature)

nat: fix update of outside fibs (output-feature)

NAT hasn't worked when NAT interfaces wasn't in
default VRF (fib_index = 0). This issue has been occurred with
interfaces with output-feature in endpoint-dependent mode.

Update VAT commands:
  - update nat44_add_del_address_range
  - add nat44_interface_add_del_output_feature

Ticket: VPP-1732
Type: fix

Change-Id: Iddea15dde4b948f159a0056d48c55bd917037fd1
Signed-off-by: Dmitry Vakhrushev <[email protected]>
(cherry picked from commit 6c57a4a985a1e4a49d1aeaf2684166cf2e122cfb)