Fix snapshot automounting with GrSecurity constify plugin.

Fix snapshot automounting with GrSecurity constify plugin.

./configure erroneously detects absence of dops->d_automount
when built against a GrSecurity patched kernel.

Summerized error message found in config.log:

  checking whether dops->d_automount() exists
  ...
  In function 'main': ... error: constified variable 'dops'
  cannot be local

The "dops" variable cannot be a local variable, so it's
moved to the global scope.

This test also fails if the prototype of the dops->d_automount
function pointer is changed.

Signed-off-by: Massimo Maggi <massimo@mmmm.it>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Richard Yao <ryao@cs.stonybrook.edu>
Closes #884