Lock the new map in vmspace_fork(). The newly allocated map should not be accessible outside vmspace_fork() yet, but locking it would satisfy the protocol of the vm_map_entry_link() and other functions called from vmspace_fork().
Lock the new map in vmspace_fork(). The newly allocated map should not
be accessible outside vmspace_fork() yet, but locking it would satisfy
the protocol of the vm_map_entry_link() and other functions called
from vmspace_fork().

Use trylock that is supposedly cannot fail, to silence WITNESS warning
of the nested acquisition of the sx lock with the same name.

Suggested and reviewed by:	tegge

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase