test/iscsi_tgt: increase memory for nvmf_tgt app

The iscsi fio_remote_nvme test was failing because the large malloc bdev
was consuming too many contiguous hugepages and the call to
construct_nvmf_subsystem was failing on some machines. This change increases the memory
allocated for the nvmf_tgt app which solves that problem.

Change-Id: Ibc882d83c5b983baee9b004bfc0970562f7f2e1f
Signed-off-by: Seth Howell <seth.howell@intel.com>
Reviewed-on: https://review.gerrithub.io/390320


Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Daniel Verkamp <daniel.verkamp@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>