Add support of SGMII SFP modules to the sfpswitch daemon.
The daemon has to read I2C EEPROM in the SFP module to determine module
type. If the module seems to be 1000BASE-T, then set it to SGMII mode.

Refacotr sfpswitch script in order to reuse code.
Add support for better --oneshot (set SFP, do not daemonize)
Add support for --resetled (Reset LED status, do not touch SFP mode,
do not daemonize).

Add LED indication to the sfpswitch daemon for Omnia.
The WAN LED has to be driven by software when SFP is inserted.
LED lights when the LOS and FLT signals are inactive.
The DIS signal has to be set to inactive.

The sfpswitch daemon has to bring the NIC down for sure before
calling network restart.

Add safety timeout to be sure the network down/up happens after
the switch is comitted to the kernel.

Omnia has GPIO expander that generates IRQs when the SFP is inserted or
removed.

mvneta driver in Omnia kernel is hacked to export attribute that sets
the target PHY. Catch is that interface has to be restarted after a switch
of the target PHY has happened.

This daemon connects this together: It waits for IRQ (in fact for GPIO
change) and performs the PHY switch and restart of network.

This is only a temporary solution for the meantime between Omnia release
and phylink driver adoption.

Important fixes:
* not trying to remove lock before I lock it
* fixed delete and mount of multiple snapshots
* fixed modify command

Few changes:
* ignoring errors in cleanup function
* recording date just in case
* more intuitive description in create command

One new feature:
* new diff command

In schnapps it would be really handy to extract to snapshot we are about to
boot, not to the root.

Make cert-bakup behave differently if btrfs is found and use specific subvolume
for backup of certificates.

Simple btrfs snapshots management tool.