um: Mark non-vector net transports as obsolete

UML_NET_VECTOR now supports filters compiled with pcap outside of UML;
it also supports: EoGRE, EoL2TPv3, RAW (+/- BPF), TAP and BESS.

While vector drivers are not 1:1 replacements for the existing drivers,
you can achieve the same topologies and the same connectivity at much
higher performance (2.5 to 9 Gbit on mid-range Ryzen desktop) - the old
drivers test out in the 500Mbit range on the same hardware.

For all these reasons, the non-vector based transports are now
unnecessary, and some, most notably pcap and vde are maintenance
burdens. Thus, it makes sense to at least start thinking about removing
the non-vector transports, so for now, mark them as obsolete.

Link: https://lore.kernel.org/lkml/15f048d3-07ab-61c1-c6e0-0712e626dd33@cambridgegreys.com/T/#u


Suggested-by: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Richard Weinberger <richard@nod.at>