KVM: VMX: Update MTF and ICEBP comments to document KVM's subtle behavior

KVM: VMX: Update MTF and ICEBP comments to document KVM's subtle behavior

Document the oddities of ICEBP interception (trap-like #DB is intercepted
as a fault-like exception), and how using VMX's inner "skip" helper
deliberately bypasses the pending MTF and single-step #DB logic.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Link: https://lore.kernel.org/r/20220830231614.3580124-24-seanjc@google.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>