FIX: vpp not started with configuration for nat44ed with 16M sessions

- after merge of commit vppinfra: use heap to store bihash data |
   https://gerrit.fd.io/r/c/vpp/+/29099
  it is necessary to allocate 14GB of memory for main heap in case
  of nat44ed test with 16.5M sessions

Change-Id: I65dccdd4f50382b1b40cdffd2d9031ffb7d3bfa1
Signed-off-by: Jan Gelety <jgelety@cisco.com>