Fix pppoe_softc_list #91

Job	Run time
Info	2s
x86_64-windows-gnu(win7)	2m 13s
x86_64-macos-none	3m 10s
x86-windows-gnu(win7)	2m 3s
aarch64-macos-none	1m 41s
x86_64-windows-gnu	4m 17s
x86-windows-gnu	3m 38s
aarch64-windows-gnu	3m 29s
x86_64-linux-musl	3m 24s
aarch64-linux-musl	2m 42s
arm-linux-musleabi(cortex_a7)	2m 48s
arm-linux-musleabi(mpcorenovfp)	2m 43s
arm-linux-musleabi(pi_zero_w)	3m 23s
mipsel-linux-musl	2m 37s
mips-linux-musl	2m 34s
	40m 44s

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