rename struct lxc_netdev fields to match reality

rename struct lxc_netdev fields to match reality

struct lxc_netdev is used to hold information from cnfig file
about a network device/configuration.  Make the fields of this
structure to be named similarily with the config file keywords,
namely:
 s/ifname/link/ - host-side link for the device (bridge or eth0)
 s/newname/name/ - container-side ifname
It is insane to have completely different names in config file
and in structure/variable names :)

Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>