Widen the ifnet_detach_sxlock to cover the entire vnet sysuninit code.
This ensures that we can't end up having the vnet_sysuninit free the UDP
pcb while the detach code is running and trying to purge the UDP pcb.
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D28530
Move the kernel space content of some Newlib provided header files to
RTEMS and libbsd. This allows to use the Newlib provided header files
with different FreeBSD baselines.
Update #3472.