Zero the un-used portions of the struct sockaddr data before sending

Zero the un-used portions of the struct sockaddr data before sending
it back to userspace, so it does not break bind(2) on raw sockets in jails.

Currently some processes, like traceroute(8) construct a routing request
to determine its source address based on the destination. This sockaddr
data is fed directly to bind(2). When bind calls ifa_ifwithaddr(9) to
make sure the address exists on the interface, the comparison will
fail causing bind(2) to return EADDRNOTAVAIL if the data wasnt zero'ed
before initialization.

Approved by:	bmilekic (mentor)