This issue seems to affect not only ODROID-U3 but many other devices and seems to be present on multiple OS too (Arch Linux ARM in my case).
What happen is that after some hours/days of intense network traffic (e.g. a torrent client installed on the board) the system logs are flooded with errors and a page allocation error occurs which results in a network disconnection.
In my case the tool journalctl report a moltitude of smsc95xx 1-2:1.0 eth0: kevent 2 may have been dropped errors.
The workarounds that should (time will tell…) solve the issue consist in creating a file named for example smsc.conf in /etc/modprobe.d and put in it the following string: smsc95xx turbo_mode=N
Disabling turbo mode will prevent the network adapter from sending multiple frames at the same time, single file copy performace in my case is invariated (9.4 MB/s ~) with and without turbo mode and the errors from syslogs are completely gone.