fix(inputs.ping): Check addr length to avoid crash

[powersj]

Summary

This will check the length of the slice to avoid a crash and moves this set up to Gather and out of Init to allow continued operation.

Checklist

• No AI generated code was used in this PR

Related issues

fixes: #15591

[telegraf-tiger]

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Artifact URLs

DEB	RPM	TAR GZ	ZIP
amd64.deb	aarch64.rpm	darwin_amd64.tar.gz	windows_amd64.zip
arm64.deb	armel.rpm	darwin_arm64.tar.gz	windows_arm64.zip
armel.deb	armv6hl.rpm	freebsd_amd64.tar.gz	windows_i386.zip
armhf.deb	i386.rpm	freebsd_armv7.tar.gz
i386.deb	ppc64le.rpm	freebsd_i386.tar.gz
mips.deb	riscv64.rpm	linux_amd64.tar.gz
mipsel.deb	s390x.rpm	linux_arm64.tar.gz
ppc64el.deb	x86_64.rpm	linux_armel.tar.gz
riscv64.deb		linux_armhf.tar.gz
s390x.deb		linux_i386.tar.gz
		linux_mips.tar.gz
		linux_mipsel.tar.gz
		linux_ppc64le.tar.gz
		linux_riscv64.tar.gz
		linux_s390x.tar.gz

[srebhan]

@powersj is there a way to detect the case where the interface goes down? I'm asking because when given the name, the interface might have another IP when coming up next time...

Approving anyway in case you think this is a premature optimization...

[powersj]

I'm asking because when given the name, the interface might have another IP when coming up next time...

Ah good point - We would need to see if the error message had anything about the interface being down, otherwise probably not. I'm going to land as this was already an issue before since we were setting the address in init before, but if someone brings this up we can revisit.