dist/tools/pyterm: ipv6 address support for tcp_serial option

[hugueslarrive]

Contribution description

Trying to connect to telnet server module with pyterm:

$ ./dist/tools/pyterm/pyterm -ts [fe80::a413:5bff:feac:60b0%enp0s25]:23
Twisted not available, please install it if you want to use pyterm's JSON capabilities
2021-08-12 22:31:02,270 # Connect to [fe80:
2021-08-12 22:31:02,274 # [Errno -2] Name or service not known
2021-08-12 22:31:02,275 # Something went wrong connecting to localhost:[fe80::a413:5bff:feac:60b0%enp0s25]:23

Testing procedure

$ ./dist/tools/pyterm/pyterm -ts [fe80::a413:5bff:feac:60b0%enp0s25]:23
Twisted not available, please install it if you want to use pyterm's JSON capabilities
2021-08-12 22:38:26,894 # Connect to fe80::a413:5bff:feac:60b0%enp0s25:23
Welcome to pyterm!
Type '/exit' to exit.
version
2021-08-12 22:38:32,398 # version
2021-08-12 22:38:32,449 # 2014.01-34120-g69dde-gnrc_sock_tcp-telnet
>

Issues/PRs references

See also #16723

[benpicco]

Looks good to me!