bugfix: use buffered channel for signal notifications

[SataQiu]

What type of PR is this?

/kind bug

What this PR does / why we need it:

bugfix: use buffered channel for signal notifications

When I upgrade to go 1.17, executing make will cause an error:

# go version
go version go1.17.1 darwin/amd64
# make
go fmt ./pkg/... ./cmd/...
pkg/yurthub/network/dummyif_test.go
pkg/yurthub/network/dummyif_unsupported.go
go vet ./pkg/... ./cmd/...
# github.com/openyurtio/openyurt/cmd/yurt-tunnel-server
cmd/yurt-tunnel-server/server.go:39:2: misuse of unbuffered os.Signal channel as argument to signal.Notify
make: *** [vet] Error 2

FYI: https://github.com/golang/go/blob/ee91bb83198f61aa8f26c3100ca7558d302c0a98/src/os/signal/example_test.go#L14-L17

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

NONE

other Note

[rambohe-ch]

/lgtm
/approve

[openyurt-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: rambohe-ch, SataQiu

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