maint: fix comma style issues: nwfilter
    
    Most of our code base uses space after comma but not before;
    fix the remaining uses before adding a syntax check.
    
    * src/nwfilter/nwfilter_ebiptables_driver.c: Consistently use
    commas.
    * src/nwfilter/nwfilter_gentech_driver.c: Likewise.
    * src/nwfilter/nwfilter_learnipaddr.c: Likewise.
    * src/conf/nwfilter_conf.c: Likewise.
    
    Signed-off-by: Eric Blake <eblake@redhat.com>