[IPV6]: Fix source address selection.

[IPV6]: Fix source address selection.

Two additional labels (RFC 3484, sec. 10.3) for IPv6 addreses
are defined to make a distinction between global unicast
addresses and Unique Local Addresses (fc00::/7, RFC 4193) and
Teredo (2001::/32, RFC 4380). It is necessary to avoid attempts
of connection that would either fail (eg. fec0:: to 2001:feed::)
or be sub-optimal (2001:0:: to 2001:feed::).

Signed-off-by: Łukasz Stelmach <stlman@poczta.fm>
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>