bhyve: [snapshot] Remove init_snapshot() and initialize static vars directly

[gusev.vitaliy_gmail.com]

Summary

vCPU-s threads are starting before init_snapshot() is called. That can lead
to VM hangs in waiting of userspace vcpu_lock mutex.

init_snapshot() only initializes static variables (mutex, cv) and that code can be
optimized and removed.

Fixes: 9a9a248964696 ("bhyve: init checkput before caph_enter")

Sponsored by: vStack

Test Plan

Compile bhyve with BHYVE_SNAPSHOT.

Run VM with 8 vCPU-s:

bhyve \
        -AHPw \
        -c 8 -m 128M \
        -s 0,hostbridge \
        -s 31,lpc \
        -l com1,stdio \
        -l bootrom,/usr/local/share/uefi-firmware/BHYVE_UEFI_CODE.fd \
        efi

Run several times and each time type "reset" command in UEFI shell.

Without patch UEFI shell sometimes hangs after "reset" command and bhyve vCPU threads are trying to acquire userspace vcpu_lock mutex-es (snapshot.c).

Patched version works as expected.

[markj]

Please mail me git format-patch output and I'll apply it.

[gusev.vitaliy_gmail.com]

rG7de582874eb9d08f3f87d11ed9e2b9ce8306db79