vmbus: delay interrupt creation until open response #1475

Job	Run time
build and check docs [x64-windows]	9m 15s
build artifacts [x64-linux]	5m 55s
build openhcl [aarch64-linux]	5m 2s
build mdbook guide	1m 24s
build openhcl [x64-linux]	7m 49s
clippy [windows], unit tests [x64-windows]	10m 42s
clippy [linux, macos], unit tests [x64-linux]	8m 5s
clippy [linux-musl, misc nostd], unit tests [x64-linux-musl]	7m 14s
unit tests [aarch64-windows]	6m 49s
build and check docs [x64-linux]	2m 50s
test flowey local backend	3m 7s
xtask fmt (linux)	2m 28s
build artifacts (not for VMM tests) [aarch64-windows]	5m 45s
build artifacts (for VMM tests) [aarch64-windows]	8m 53s
build artifacts (not for VMM tests) [x64-windows]	6m 2s
build artifacts (for VMM tests) [x64-windows]	9m 49s
build artifacts [aarch64-linux]	5m 28s
xtask fmt (windows)	7m 2s
run vmm-tests [aarch64-windows]	6m 31s
run vmm-tests [x64-windows-amd]	11m 25s
run vmm-tests [x64-windows-intel]	9m 23s
run vmm-tests [x64-linux]	3m 44s
openvmm checkin gates	6s
	2h 24m 48s

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