VPP static NAT without destination IP address unexpected behavior
To reproduce
```
set interfaces ethernet eth0 address '192.168.122.14/24'
set interfaces ethernet eth0 description 'WAN'
set interfaces ethernet eth1 address '192.0.2.1/24'
set vpp settings interface eth0 driver 'dpdk'
set vpp settings interface eth1 driver 'dpdk'
set vpp settings unix poll-sleep-usec '120'
set vpp nat44 static rule 10 inbound-interface 'eth0'
set vpp nat44 static rule 10 outbound-interface 'eth1'
set vpp nat44 static rule 10 protocol 'tcp'
set vpp nat44 static rule 10 translation address '192.0.2.2'
```
We get:
```
vyos@r14:~$ show vpp nat44 static
Des_address/interface Dest_port Trans_address Trans_port Protocol
----------------------- ----------- --------------- ------------ ----------
192.0.2.1 192.0.2.2 tcp
eth1 192.0.2.2 tcp
vyos@r14:~$
```
We expect:
All traffic that is incoming on WAN interface `eth0` is translated to the internal address `192.0.2.2`
If we add the destination address, output looks correct:
```
vyos@r14# set vpp nat44 static rule 10 destination address 192.168.122.111
[edit]
vyos@r14# commit
vyos@r14# run show vpp nat44 static
Des_address/interface Dest_port Trans_address Trans_port Protocol
----------------------- ----------- --------------- ------------ ----------
192.168.122.111 192.0.2.2 tcp
[edit]
vyos@r14#
```