ltq-vdsl-app: add ubus support to get metrics

ltq-vdsl-app: add ubus support to get metrics

Add a 'dsl' ubus object with a 'metrics' function to replace the
expensive shell parsing done by /etc/init.d/dsl_control [dsl|luci]stat.

All metrics are gathered by using syscalls. An additional thread is started
to handle ubus events.

$ time /etc/init.d/dsl_control dslstat
real	0m 2.66s
user	0m 0.90s
sys	0m 1.76s

$ time ubus call dsl metrics
real	0m 0.02s
user	0m 0.00s
sys	0m 0.01s

Example output:
{
	"api_version": "4.17.18.6",
	"firmware_version": "5.8.1.5.0.7",
	"chipset": "Lantiq-VRX200",
	"driver_version": "1.5.17.6",
	"state": "Showtime with TC-Layer sync",
	"up": true,
	"uptime": 3891,
	"atu_c": {
		"vendor_id": [
			181,
			0,
			66,
			68,
			67,
			77,
			178,
			26
		],
		"vendor": "Broadcom 178.26",
		"system_vendor_id": [
			181,
			0,
			66,
			68,
			67,
			77,
			0,
			0
		],
		"system_vendor": "Broadcom",
		"version": [
			49,
			57,
			46,
			48,
			46,
			51,
			53,
			46,
			50,
			32,
			86,
			69,
			95,
			49,
			49,
			95
		],
		"serial": [
			65,
			65,
			49,
			52,
			52,
			54,
			70,
			69,
			48,
			90,
			87,
			45,
			48,
			56,
			0,
			0,
			0,
			0,
			0,
			0,
			0,
			0,
			0,
			0,
			0,
			0,
			0,
			0,
			0,
			0,
			0,
			0
		]
	},
	"power_state": "L0 - Synchronized",
	"xtse": [
		0,
		0,
		0,
		0,
		0,
		0,
		0,
		2
	],
	"annex": "B",
	"standard": "G.993.2",
	"profile": "17a",
	"mode": "G.993.2 (VDSL2, Profile 17a, with down- and upstream vectoring)",
	"upstream": {
		"vector": true,
		"trellis": true,
		"bitswap": true,
		"retx": true,
		"virtual_noise": false,
		"interleave_delay": 0,
		"data_rate": 31999000,
		"latn": 8.500000,
		"satn": 8.400000,
		"snr": 12.700000,
		"actps": -90.100000,
		"actatp": 13.400000,
		"attndr": 37180000
	},
	"downstream": {
		"vector": true,
		"trellis": true,
		"bitswap": true,
		"retx": true,
		"virtual_noise": false,
		"interleave_delay": 140,
		"data_rate": 89998000,
		"latn": 9.500000,
		"satn": 9.600000,
		"snr": 13.300000,
		"actps": -90.100000,
		"actatp": -1.600000,
		"attndr": 116315372
	},
	"errors": {
		"near": {
			"es": 1,
			"ses": 0,
			"loss": 3,
			"uas": 424,
			"lofs": 0,
			"fecs": 0,
			"hec": 0,
			"ibe": 0,
			"crc_p": 0,
			"crcp_p": 0,
			"cv_p": 0,
			"cvp_p": 0,
			"rx_corrupted": 27740,
			"rx_uncorrected_protected": 27010,
			"rx_retransmitted": 0,
			"rx_corrected": 730,
			"tx_retransmitted": 16222
		},
		"far": {
			"es": 242,
			"ses": 71,
			"loss": 0,
			"uas": 424,
			"lofs": 0,
			"fecs": 22687,
			"hec": 0,
			"ibe": 0,
			"crc_p": 0,
			"crcp_p": 0,
			"cv_p": 0,
			"cvp_p": 0,
			"rx_corrupted": 1383552,
			"rx_uncorrected_protected": 1220215,
			"rx_retransmitted": 0,
			"rx_corrected": 163337,
			"tx_retransmitted": 1574051
		}
	}
}

Signed-off-by: Andre Heider <a.heider@gmail.com>
Tested-by: Martin Schiller <ms@dev.tdt.de>