KVM: selftests: Extend state_test to check next_rip

KVM: selftests: Extend state_test to check next_rip

Similar to vGIF, extend state_test to make sure that next_rip is saved
correctly in nested state. GUEST_SYNC() in L2 causes IO emulation by
KVM, which advances the RIP to the value of next_rip. Hence, if next_rip
is saved correctly, its value should match the saved RIP value.

Signed-off-by: Yosry Ahmed <yosry@kernel.org>
Link: https://patch.msgid.link/20260225005950.3739782-5-yosry@kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>