luci-mod-status: extend DSL metrics

Add the following metrics:

- Bitswap and rate adaptation status
- Impulse noise protection (INP)
- Retransmission status (G.INP)
- Channel error counters (CV-C, FEC-C)
- G.INP counters (MINEFTR, LEFTRS, rtx-tx, rtx-c, rtx-uc)
- Modem chipset and firmware version

Signed-off-by: Jan Hoffmann <jan@3e8.eu>