Delay permission checks for VCHR vnodes until after vnode is locked in vm_mmap_vnode function, where we can safely check for a special /dev/zero case. Rev. 1.180 has reordered checks and introduced a regression.
Delay permission checks for VCHR vnodes until after vnode is locked in
vm_mmap_vnode function, where we can safely check for a special /dev/zero
case. Rev. 1.180 has reordered checks and introduced a regression.

Submitted by:	alc
Was broken by:	kan

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