security/tinc: External address fields won't accept IPv6

[vnxme]

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[+] I have read the contributing guide lines at https://github.com/opnsense/plugins/blob/master/CONTRIBUTING.md

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Describe the bug
The external address fields both on the network and host configuration pages of Tinc won't accept IPv6.

To Reproduce
Steps to reproduce the behavior:

1. Go to VPN->Tinc->Configuration->Networks
2. Click on 'plus' (Add a new network configuration) or 'pencil' (Edit an existing network configuration)
3. Fill in relevant information including IPv6 in the 'Ext. Address' field
4. Click 'Save'
5. See error next to the 'Ext. Address' field
6. The same applies to creating a new host or editing an existing one

Expected behavior
As stated in the help text, the field should accept IPv6 as well as IPv4 and hostnames.

Screenshots
Please, do not be confused by these link local addresses. It does not matter what type of address to fill, the field simply won't accept any IPv6 without a reason.

Relevant log files
None

Additional context
I'm sure that in previous versions this field successfully accepted IPv6. Unfortunately, I can't say exactly when it broke. According to logs, it broke for me on December 18, 2020 that is one day after the 20.7.7 version was released which included "os-tinc 1.6 enables multiple addresses per host (contributed by ElNounch)". Please, review the changes pulled in #2110.

Environment
OPNsense 20.7.7_1