net: skip TestIPv4MulticastListener on linux without CONFIG_IP_MULTICAST

[qmuntal]

What version of Go are you using (go version)?

go version go1.17.2 linux/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/root/.cache/go-build"
GOENV="/root/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/root/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/root/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/src/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/src/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.17.2"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/usr/local/src/go/src/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build4211212346=/tmp/go-build -gno-record-gcc-switches"

What did you do?

go test -run TestIPv4MulticastListener net

I'm running this command from within a Linux machine whose kernel was built without CONFIG_IP_MULTICAST.

What did you expect to see?

TestIPv4MulticastListener skipped because IP multicast is not enabled.

In fact this was already proposed by @bradfitz in #11936 (comment) but never implemented.

What did you see instead?

--- FAIL: TestIPv4MulticastListener (0.00s)
    listen_test.go:570: 224.0.0.254 not found in multicast rib
FAIL
FAIL    net     0.005s
FAIL

[mknyszek]

CC @neild