feat(interface): apply MTU for dpdk plugin ifaces

When changing MTU on a running VPP, the interface has to be down.

- Other plugins (rdma, avf, af_xdp) need vastly different logic,
  so support for them will be added later.
+ Mlx5-core does not need to set MTU on Linux interface.
+ MTU setting now does not happen at final setting path up,
  it happens in driver initialization layer instead
  E.g. AVF tests will not attempt to change MTU.
+ MTU edit removed from some non-hardware interfaces (including memif)
  e.g. bond interfaces. MTU on parent hw interface seems to be enough.
+ The non-jumbo MTU value used is 1800,
  so 1518B tests with additional encapsulation can still work.
+ When VPP MTU setting fails, the failure is now propagated.
  Previously, the failure was just logged and ignored,
  but now there is no reason to hide it.

Ticket: CSIT-1797

Change-Id: I3b853f1faf90001d544cbbb87b2affbb882ffba0
Signed-off-by: Vratko Polak <vrpolak@cisco.com>