The netif list is used like a stack, so it needs to be
iterated in reverse to keep the registration order.
Time complexity in O(n^2), but the the list is normally very short
(1-2 items).
Before:
```
> ifconfig
Iface 10 HWaddr: 24:0A:C4:E6:0E:9C Channel: 0 Link: down
[..]
Iface 7 HWaddr: 24:0A:C4:E6:0E:9F Link: down
[..]
```
Now they are in the increasing order:
```
> ifconfig
Iface 7 HWaddr: 24:0A:C4:E6:0E:9F Link: down
[..]
Iface 10 HWaddr: 24:0A:C4:E6:0E:9C Channel: 0 Link: down
[..]
```
When lwIP is hacked to use the same shell command, it also
lists it interfaces in the expected order (was ET1,ET0 before):
```
> ifconfig
Iface ET0 HWaddr: 24:0A:C4:E6:0E:9F Link: down
[..]
Iface ET1 HWaddr: 24:0A:C4:E6:0E:9C Channel: 0 Link: down
[..]
```
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