KVM: VMX: Skip filter updates for MSRs that KVM is already intercepting

When handling userspace MSR filter updates, recompute interception for
possible passthrough MSRs if and only if KVM wants to disabled
interception.  If KVM wants to intercept accesses, i.e. the associated
bit is set in vmx->shadow_msr_intercept, then there's no need to set the
intercept again as KVM will intercept the MSR regardless of userspace's
wants.

No functional change intended, the call to vmx_enable_intercept_for_msr()
really is just a gigantic nop.

Suggested-by: Aaron Lewis <aaronlewis@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220610214140.612025-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>