Current controller fails to build on i386

[Martin Gerhard Loschwitz]

While trying to have Launchpad automatically build packages for the Controller on i386, I realized that i386 builds will currently fail due to improper usage of format specifiers.

This happens in two occasions:

controller/src/bgp/community.cc
  snprintf(start, sizeof(start), "Communities: %lu [", communities.size());

controller/src/bgp/bgp_origin_vn_path.cc
  snprintf(repr, sizeof(repr), "OriginVnPath <code: %d, flags: %02x> : %lu",

The problem is %lu here, which needs to be replaced by "%z"u to make the build work properly on amd64 and i386.