Stretch release notes:
PS Raspberry Pi build-in ethernet interface is usb device.2.2.8. New method for naming network interfaces
The installer and newly installed systems will use a new standard naming scheme for network interfaces instead of eth0, eth1, etc. The old naming method suffered from enumeration race conditions that made it possible for interface names to change unexpectedly and is incompatible with mounting the root filesystem read-only. The new enumeration method relies on more sources of information, to produce a more repeatable outcome. It uses the firmware/BIOS provided index numbers and then tries PCI card slot numbers, producing names like ens0 or enp1s1 (ethernet) or wlp3s0 (wlan). USB devices, which can be added to the system at any time, will have names based upon their ethernet MAC addresses.
PPS if you update Jessie to Stretch, you have old names