This is force commit to mention about previous commit.

• added comments about why in6p_inputopts should not be copied in tcp6_input().
• call ip6_copypktopts() in order to copy in6p_outputopts from a listening PCB to a corresponding accepting one.
• be proactive about unspecified IPv6 source address. pcb layer uses unspecified address (::) to mean "unbounded" or "unconnected", and can be confused by packets from outside.
• made consist between tcp and udp in using mappedaddr
• setsockopt(BIND_IPV6ONLY) now works
• deprecated address consideration on TCP SYN.
• get rid of M_ANYCAST6