Introduce a new list option "entry" which can be used to specify entries
to add to the ipset, e.g.
config ipset
option name test
...
list entry 1.2.3.4,8080
list entry 5.6.7.8,8081
Also introduce a new option "loadfile" which refers to an external file
containing set entries to add, with one item per line.
Signed-off-by: Jo-Philipp Wich <jo@mein.io>