If there is more than one interface, print the id of the receiving
interface for convenience.
```
ping6 ff02::1
2020-02-20 18:19:38,644 # 12 bytes from fe80::d0ae:c1b:2054:58e%7: icmp_seq=0 ttl=64 rssi=-45 dBm time=4.801 ms
2020-02-20 18:19:38,652 # 12 bytes from fe80::d0ae:c1b:2054:58c%8: icmp_seq=0 ttl=64 rssi=-63 dBm time=13.422 ms (DUP!)
2020-02-20 18:19:38,661 # 12 bytes from fe80::c78:16d9:8aca:ba9a%8: icmp_seq=0 ttl=64 rssi=-44 dBm time=21.819 ms (DUP!)
2020-02-20 18:19:39,648 # 12 bytes from fe80::d0ae:c1b:2054:58e%7: icmp_seq=1 ttl=64 rssi=-44 dBm time=4.797 ms
2020-02-20 18:19:39,657 # 12 bytes from fe80::d0ae:c1b:2054:58c%8: icmp_seq=1 ttl=64 rssi=-61 dBm time=12.917 ms (DUP!)
2020-02-20 18:19:39,666 # 12 bytes from fe80::c78:16d9:8aca:ba9a%8: icmp_seq=1 ttl=64 rssi=-43 dBm time=21.679 ms (DUP!)
2020-02-20 18:19:40,657 # 12 bytes from fe80::d0ae:c1b:2054:58e%7: icmp_seq=2 ttl=64 rssi=-41 dBm time=4.795 ms
```
Having the definitions sit in the `net/gnrc/sixlowpan/frag.h` header
does not make much sense, when using Selective Fragment Forwarding
(and the fragmentation buffer already includes a
`net/gnrc/sixlowpan/frag/stats.h` header), so they are moved to their
own header. Since with this change it makes more sense to have the
statistics stored in their own sub-module, the pseudo-module is also
actualized.
Previously `ifconfig` would only know link-local addresses
(printed as 'local') and everything else would be 'global'.
This is wrong for site-local and unique local addresses which were
also denoted as global.
So use the already existing helper functions to determine the correct
type of IPv6 address when printing.
Replaces the special heap command approach of the lpc_common module with a more general heap command approach. Module lpc_common was already removed with PR #2118. PR #2118 integrated cpu/lpc_common code in cpu/lpc2387. With PR #3530 special heap handling for cpu/lpc2387 was replaced by newlib memory management which uses _sbrk_r to allocate chunks from the heap. _sbrk_r uses _sheap and _eheap symbols that are defined in lpc2387.ld and can be used together with mallinfo function for heap statistics.
