tvhdhomerun: check return values of setsockopt

This is a very small fix for the case when _setsockopt_ fails to set socket options. The return value was never checked, which may lead to use-cases where the plugin fails silently. This introduces some helpful log messages for those cases. Note that setting the rx buffer is allowed to fail: without it the user will be getting continuity errors but for some cases this might work (SD streams).