You can actually save some licensing too, just by blacklisting the field, along with it's value in inputs.conf itself.
blacklist = src_ip = 10.0.0.0/8
Else, routing the data to null queue, as explained by @mguhad, will work too. I find blacklisting the data to be more helpful, when i know I don't need a portion of data at all. Why even bother to ingest it, when it has no use.