Comment 5 for bug 50099

Mine is as follows:
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# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# This is a list of hotpluggable network interfaces.
# They will be activated automatically by the hotplug subsystem.
auto eth0

iface eth0 inet dhcp
 pre-up /sbin/ifconfig $IFACE mtu 1400

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The forum thread linked to in the first comment has others from users with the same problem.