vmm: move bumping VMEXIT_USERSPACE stat to the right place

Statistic for "number of vm exits handled in userspace" should be
increased in vm_run() instead of vmx_run() because in some cases
vm_run() doesn't exit to userspace and keeps entering the guest.

Also svm_run's implementation even wrongly misses that stat.

Reviewed by: markj

(cherry picked from commit e7d34aeda4e6fba68343dfcaf5e4aeed83a0ec87)