tcp: prevent tcp_nuke_addr from purging v4 sockets on v6 addr

Do not kill IPv4 sockets if the KILLADDR IOCTL was called with
an IPv6 address.

Change-Id: I0559c72bf8b317ddf3ab4a93dbb5c26054c9bfb3
Signed-off-by: Harout Hedeshian <harouth@codeaurora.org>