EPL: Fix for Write Multiple by index

 Write multiple by index now correctly resolves OD names.

 Changes in regard to master
   - Removed usage of proto_tree_add_subtree[_format]

Signed-off-by: Lukas Emersberger <lukas.emersberger@gmail.com>
Reviewed-on: https://code.wireshark.org/review/3223
Reviewed-by: Roland Knall <rknall@gmail.com>
Reviewed-by: Lukas Emersberger <lukas.emersberger@br-automation.co.at>
Reviewed-by: Evan Huus <eapache@gmail.com>

Change-Id: Iace0ccd042035a54fd615dcc5559e517eefd69bd
Reviewed-on: https://code.wireshark.org/review/3241
Reviewed-by: Roland Knall <rknall@gmail.com>
Reviewed-by: Lukas Emersberger <lukas.emersberger@gmail.com>
Reviewed-by: Evan Huus <eapache@gmail.com>
Petri-Dish: Evan Huus <eapache@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michael Mann <mmann78@netscape.net>