renenable out-of-tree intel ethernet driver (e1000e, igb, ixgbe)

There where just to much issues with the 4.15 in tree drivers for our
users [1]. The updated igb and ixgbe drivers are compatible with
4.15, the e1000e driver needed to be ported to the new internal
kernel timer API, which is pretty straight forward.

[1]: https://forum.proxmox.com/threads/4-15-based-test-kernel-for-pve-5-x-available.42097/page-5

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>