build, yang: bump libyang minimum required version to 1.0.184

build, yang: bump libyang minimum required version to 1.0.184

It's time to say good bye to libyang 0.16.105. The recently
released libyang 1.0.184 includes numerous bug fixes and performance
improvements that we need.

Despite the major version bump from 0.x to 1.x, the libyang API is
the same except for a single backward-incompatible change in the
user types interface (which we're currently not using). Hence no
code changes were necessary to adapt FRR to libyang 1.x.

This commit also reintroduces some leafrefs that needed to be
removed from our YANG modules due to a bug that was present on
libyang 0.16.105.

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>