selftest/net: fix protocol family to work for IPv4.

use actual protocol family passed by user rather than hardcoded
AF_INTE6 to cerate sockets.
current code is not working for IPv4.

Signed-off-by: Maninder Singh <maninder1.s@samsung.com>
Signed-off-by: Vaneet Narang <v.narang@samsung.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>