KVM: nSVM: Ensure AVIC is inhibited when restoring a vCPU to guest mode

KVM: nSVM: Ensure AVIC is inhibited when restoring a vCPU to guest mode

On nested VMRUN, KVM ensures AVIC is inhibited by requesting
KVM_REQ_APICV_UPDATE, triggering a check of inhibit reasons, finding
APICV_INHIBIT_REASON_NESTED, and disabling AVIC.

However, when KVM_SET_NESTED_STATE is performed on a vCPU not in guest
mode with AVIC enabled, KVM_REQ_APICV_UPDATE is not requested, and AVIC
is not inhibited.

Request KVM_REQ_APICV_UPDATE in the KVM_SET_NESTED_STATE path if AVIC is
active, similar to the nested VMRUN path.

Fixes: f44509f849fe ("KVM: x86: SVM: allow AVIC to co-exist with a nested guest running")
Cc: stable@vger.kernel.org
Signed-off-by: Yosry Ahmed <yosry@kernel.org>
Link: https://patch.msgid.link/20260224225017.3303870-1-yosry@kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>