Don't kill IPv4 sockets when killing IPv6 sockets was requested.

c7c3ec4903d32c60423ee013d96e94602f66042c cherry-picked the
tcp_nuke_addr ioctl, but omitted a check that ensures that a
socket is an IPv6 socket. This makes it so that if we issue a
SIOCKILLADDR on ::, it kills IPv4 sockets as well.

This is because every IPv4 socket has an IPv6 source address
(sk_v6_rcv_saddr) of ::. Thus, when we iterate over an IPv4
socket, and compare the source address of the socket to the
source address in the ioctl, it matches the :: that was passed
in, and we kill the socket.

Change-Id: I736431a898e6ec91536536d352936a210aa10100