IPv6/addrconf: Fix minor addrlabel thinko

Fix apparent thinko related to RTM_DELADDRLABEL, introduced by commit
2a8cc6c8 ("[IPV6] ADDRCONF: Support
RFC3484 configurable address selection policy table.").

Signed-off-by: Tushar Gohad <tgohad@mvista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>