vmm: move bumping VMEXIT_USERSPACE stat to the right place

[gusev.vitaliy_gmail.com]

Summary

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.

Test Plan

Getting statistic since boot&halt before patching

~# bhyvectl --get-stat --vm=$VM | grep userspace

number of vm exits handled in userspace 	228650

Geting statistic since boot&halt after patching

~# bhyvectl --get-stat --vm=$VM | grep userspace

number of vm exits handled in userspace 	139744

[gusev.vitaliy_gmail.com]

@markj Could you commit it?