Load bridge module

This patch makes sure bridge module is loaded and net.bridge* config
is loaded or makes sysctl fail if it is not loaded.

Reverts If7c0bb538bd0fa995e1fd6a72105d6415ae78ee5 which only hides
this issue and actually solves nothing.

Change-Id: I762f6a88ad4a19d720d762357b71e877315ea182
Fixes: rhbz#1123465
(cherry picked from commit 1151170f534b2e44d9dd3549befa0021e01a1b74)