um: Make CONFIG_STATIC_LINK actually static

Currently, CONFIG_STATIC_LINK can be enabled with options which cannot
be statically linked, namely UML_NET_VECTOR, UML_NET_VDE, and
UML_NET_PCAP; this is because glibc tries to load NSS which does not
support being statically linked. So make CONFIG_STATIC_LINK depend on
!UML_NET_VECTOR && !UML_NET_VDE && !UML_NET_PCAP.

Link: https://lore.kernel.org/lkml/f658f317-be54-ed75-8296-c373c2dcc697@cambridgegreys.com/#t


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