Make accepted sockets inherit IP_TTL from the listening socket.

Make accepted sockets inherit IP_TTL from the listening socket.

This is consistent with the IPV6_UNICAST_HOPS behavior, and is the only
way to allow applications to completely control the TTL of outgoing
packets (else an application could temporariy send packets with the
default TTL, until it sets again IP_TTL ; this is harmful eg for GTSM).

ok bluhm@