luci-mod-admin-full: extend dsl stats

luci-mod-admin-full: extend dsl stats

This adds a lot of new status information about the dsl line.
It now looks like this on a Telekom line:

Status: UP
Line State: showtime_tc_sync [0x801]
Line Mode: G.993.2 (VDSL2)
Annex: B
Profile: 17a
Data Rate: 51.391 Mb/s / 10.046 Mb/s
Max. Attainable Data Rate (ATTNDR): 63.817 Mb/s / 23.908 Mb/s
Latency: 4.0 ms / 8.0 ms
Line Attenuation (LATN): 10.5 dB / 9.9 dB
Signal Attenuation (SATN): 8.2 dB / 14.4 dB
Noise Margin (SNR): 10.5 dB / 9.7 dB
Aggregate Transmit Power(ACTATP): -14 dB / 12.4 dB
Forward Error Correction Seconds (FECS): 1 / 1723485
Errored seconds (ES): 0 / 2477
Severely Errored Seconds (SES): 0 / 50
Loss of Signal Seconds (LOSS): 0 / 0
Unavailable Seconds (UAS): 31 / 31
Header Error Code Errors (HEC): 0 / 0
Non Pre-emtive CRC errors (CRC_P): 0 / 0
Pre-emtive CRC errors (CRCP_P): 0 / 0
Line Uptime: 2m 3s
ATU-C System Vendor ID: Broadcom 176.15
Power Management Mode: L0 - Synchronized

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>