shell/cmds: add udptty command

[benpicco]

Contribution description

To facilitate remote debugging in isolated networks, we need a RIOT client for stdio_udp.
This adds a udptty command that fulfills this role.

Testing procedure

On one board, enable the stdio_udp module, on the other board enable the shell_cmd_udptty module.

You can now connect to the remote board from within RIOT:

> ifconfig
Iface  6  HWaddr: 7A:37:FC:7D:1A:AF 
          L2-PDU:1500  MTU:1500  HL:64  Source address length: 6
          Link type: wired
          inet6 addr: fe80::7837:fcff:fe7d:1aaf  scope: link  VAL
          inet6 group: ff02::1
          inet6 group: ff02::1:ff7d:1aaf
          inet6 group: ff02::1a
          
          Statistics for Layer 2
            RX packets 5  bytes 542
            TX packets 2 (Multicast: 2)  bytes 140
            TX succeeded 0 errors 0
          Statistics for IPv6
            RX packets 5  bytes 472
            TX packets 2 (Multicast: 2)  bytes 112
            TX succeeded 2 errors 0

> udptty fe80::58b0:8ff:fe67:ad82 2323
> ifconfig
6 HWaddr: 5A:B0:08:67:AD:82 
          L2-PDU:1500  MTU:1500  HL:64  Source address length: 6
          Link type: wired
          inet6 addr: fe80::58b0:8ff:fe67:ad82  scope: link  VAL
          inet6 group: ff02::1
          inet6 group: ff02::1:ff67:ad82
          inet6 group: ff02::1a
                    Statistics for Layer 2
            RX packets 10  bytes 808
            TX packets 157 (Multicast: 4)  bytes 12044
            TX succeeded 0 errors 0
          Statistics for IPv6
            RX packets 10  bytes 668
            TX packets 158 (Multicast: 4)  bytes 10055
            TX succeeded 158 errors 0

Issues/PRs references

[maribu]

some suggestions inline, otherwise lgtm

[riot-ci]

Murdock results

✔️ PASSED

13deed1 shell/cmds: add udptty command

Success	Failures	Total	Runtime
8627	0	8627	08m:37s

Artifacts

• Documentation preview