randpkt: fix no previous prototype for 'randpkt_*' [-Wmissing-prototypes]

randpkt: fix no previous prototype for 'randpkt_*' [-Wmissing-prototypes]

randpkt.c:556:1: warning: no previous prototype for ‘randpkt_seed’
randpkt.c:610:6: warning: no previous prototype for ‘randpkt_example_init’
randpkt.c:632:6: warning: no previous prototype for ‘randpkt_example_close’
randpkt.c:638:6: warning: no previous prototype for ‘randpkt_loop’

Change-Id: Ieab604a22fa7ebf5c049ab497abd56af0a788d36
Reviewed-on: https://code.wireshark.org/review/11654
Petri-Dish: Alexis La Goutte <alexis.lagoutte@gmail.com>
Reviewed-by: Dario Lombardo <lomato@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Reviewed-by: Michael Mann <mmann78@netscape.net>