libnm-core: fix team link-watcher struct layout

As the comment above the union says, structs in the union must have
the same layout of arp_ping. 'vlanid' is in the wrong place and breaks
that.

Fixes: f44c793f

#110
5 jobs for bg/issue110 in 17 minutes and 5 seconds (queued for 2 seconds)
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checkpatch

00:04:34

passed #90487
f28_build_autotools

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passed #90488
f28_build_meson

00:03:40

passed #90489
f28_rpm_autotools_dbg

00:15:38

passed #90490
f28_rpm_meson_dbg

00:13:34