nat: nat44 cli bug fix

nat: nat44 cli bug fix

Two similar CLI paths "nat44" and "nat44 add interface address"
caused unexpected behavior. If "nat44 add interface address"
command would fail the vlib cli processing function would
call "nat44" handler. This would also clean any previously
set errors from the first command and basically return
same error returned by "nat44" handler for every failed
command that starts with the same path string.

Fixes nat44-ed and nat44-ei plugin.

Change-Id: I1aac85c8ae2932da582a2b78243521d1bf8a0653
Ticket: VPP-2021
Type: fix
Signed-off-by: Filip Varga <fivarga@cisco.com>