sharing: Bind hostname_entry from UI

The entry was not bound. Due to this we could run into a segfault trying
to query the hostname_entry. This would only happen if avahi is not
running.

Fixes #178
11 jobs for benzea/fix-avahi-sharing-crash in 6 minutes and 53 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Build
passed #108616
build

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  Test
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asan

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ppc64le
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tsan
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  Review
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