The typo for the "connection_host" configuration parameter in [udp://] stanzas of inputs.conf is indeed misreported and we currently have a bug opened to fix this problem (SPL-38051). This will be fixed in version 4.2.1
If you require an immediate work-around, simply add the following line to $SPLUNK_HOME/etc/system/README/inputs.conf.spec at line 432, under the options defined for [udp://] stanzas :
connection_host = [ip|dns|none]
This will prevent any further false positives on "connection_host".
If you want to know more about how keys in configuration files are checked in 4.2, take a look at this Splunk Answer.