fix(inputs.modbus): add slave id to failing connection

[MyaLongmire]

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resolves #12021

[powersj]

This is a helpful change, but does this also actually resolve #12021? The error message the user shows is unwrapped, and I believe it is coming from the top of Gather() where there is a call to m.connect() and an unwrapped connect error.

[srebhan]

Looks good to me. Thanks @MyaLongmire!

[MyaLongmire]

@powersj the top of the gather connecting is not due to 1 slave having issues. That would come from a gateway device having problems connecting. In that case, he should use an alias to determine which gateway he is having problems with. I asked him to test the artifacts and recommended using an alias.

[telegraf-tiger]

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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_i386.zip
armel.deb	armv6hl.rpm	freebsd_amd64.tar.gz
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
		static_linux_amd64.tar.gz

[powersj]

Given the closure of the original bug I'm going to merge this :)