Adds "v4-defaultroute-replace" config/command-line setting (default disabled).
When enabled, it will unconditionally disable the pre-flight IPv4 connectivity
check, and ensure that any pre-existing IPv4 default routes are removed during
startup (and presumably replaced with the one pointing to the CLAT, unless
"v4-defaultroute-enable" has been disabled). Any IPv4 default routes that were
removed in this manner are restored when clatd is shutting down.
This allows clatd to work correctly on 3GPP mobile networks, where the
IID is assigned from the network, rather than being generated using
EUI-64. We still prefer the old method, though, the random one is only
used if no EUI-64 address exists on the PLAT device. Update docs
accordingly.
Also upgrade docs to better describe usage as a SIIT-DC Host Agent.
Tore Anderson