Do not skip scope zone violation check, when mbuf has M_FASTFWD_OURS flag.

When mbuf has M_FASTFWD_OURS flag, this means that a destination address
is our local, but we still need to pass scope zone violation check,
because protocol level expects that IPv6 link-local addresses have
embedded scope zone indexes. This should fix the problem, when ipfw is
used to forward packets to local address and source address of a packet
is IPv6 LLA.

Reported by: sbruno
MFC after: 3 weeks