Log Message:
Add u6rd-1.7.1 based on packaging provided in PR#47254

u6rd is a user-space 6rd (RFC 5569) implementation, which uses
tun(4) and the raw socket interface.

It runs on the 6rd border router of a 6rd site that is isolated from
the native IPv6 Internet.  In other words, it does not provide the
functionality of 6rd "relay" routers.