initrd: add support for rd.net.timeout.carrier
Add support for carrier-wait-timeout setting from kernel cmdline.
This will create a new 15-carrier-timeout.conf file in
/run/NetworkManager/conf.d with the parameter value as specified.
The setting also inserts match-device to *, matching all devices.
NB: The parameter on kernel cmdline is specified in seconds. This is done to be backwards compatible with with network-legacy module. However the generated setting will automatically multiply specified value by 1000 and store timeout value in ms.