modified:   src/libdpdkif/dpdkif_user.c

Modifications made to make dpdkif_user work with the vmxnet3 driver:
-No support for TX Multisegments
-No support for TX Offload
-The vmxnet3 needs at least 512 TX descriptors and recommends at least 256 RX descriptor
-The amount of mbufs in the defined rx&tx pools should contain equal amount of rx or tx descriptors + a certain amount extra to cope with packets bursts