To support lwIP better (dont require gnrc_ipv6)

Also don't require IPv6 for printing link type

With this sc_gnrc_netif can compile and work when using lwIP
(with l2util module added):

```
> ifconfig
Iface  ET1  HWaddr: 24:0A:C4:E6:0E:9C  Channel: 6  Link: up
          L2-PDU:1500  Source address length: 6
          Link type: wireless
          inet6 addr: fe80::260a:c4ff:fee6:e9c  scope: link
          inet6 addr: 2001:db8::260a:c4ff:fee6:e9c  scope: global

Iface  ET0  HWaddr: 24:0A:C4:E6:0E:9F  Link: up
          L2-PDU:1500  Source address length: 6
          Link type: wired
          inet6 addr: fe80::260a:c4ff:fee6:e9f  scope: link
          inet6 addr: 2001:db8::260a:c4ff:fee6:e9f  scope: global

>
```

Still works in gnrc_networking example:

```
> ifconfig
Iface  8  HWaddr: 24:0A:C4:E6:0E:9F  Link: up
          L2-PDU:1500  MTU:1500  HL:64  RTR
          RTR_ADV
          Source address length: 6
          Link type: wired
          inet6 addr: fe80::260a:c4ff:fee6:e9f  scope: link  VAL
          inet6 group: ff02::2
          inet6 group: ff02::1
          inet6 group: ff02::1:ffe6:e9f
          inet6 group: ff02::1a
```

To avoid dependency on gnrc files.
As suggested in RIOT-OS#16965