rpc: take a file-scope copy of some RPC procedures

The original may be freed out from underneath us if a duplicate is registered.
Thanks to Bruce Fields for pointing out one case of this I'd missed.

Also replace a bunch of manual "foo.field = 0" with just wmem_new0() instead.

Bug: 10636
Change-Id: I342bd732f062b0a191cbbf5ae417356385d2fd53
Reviewed-on: https://code.wireshark.org/review/5046
Petri-Dish: Evan Huus <eapache@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Evan Huus <eapache@gmail.com>