net: ipv6: add missing lock in ping_v6_sendmsg

Bug: 9469865
Change-Id: I5e9db559d22e35d27fa1df948b70c70ed8b42115
Signed-off-by: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Conflicts:

	net/ipv6/ping.c