Finally fixed :D
Thank you very much.
/etc/udev/rules.d/70-persistent-net.rules had the entry
# PCI device 0x8086:0x107c (e1000)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:1b:21:4d:a1:d1", ATTR{type}=="1", KERNEL=="eth*", NAME="eth1"
which I changed to eth0.