[IPV6]: Don't forward packets to proxied link-local address.

Proxying router can't forward traffic sent to link-local address, so signal
the sender and discard the packet. This behavior is clarified by Mobile IPv6
specification (RFC3775) but might be required for all proxying router.
Based on MIPL2 kernel patch.

Signed-off-by: Ville Nuorvala <vnuorval@tcs.hut.fi>
Signed-off-by: Masahide NAKAMURA <nakam@linux-ipv6.org>
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>