net: ipv6: addrlabel: fix spelling mistake "requewst" -> "request"

There is a spelling mistake in a NL_SET_ERR_MSG_MOD error message,
fix it.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>