net/null: fix secondary burst function selection

net/null: fix secondary burst function selection

Secondary process uses the primary process device and while setting the
Rx/Tx functions it uses the device arguments from the secondary process
instead of the primary ones.

This may cause primary and secondary process use different Rx/Tx
functions unintentionally.

Fixes: bccc77a6a74a ("net/null: fix multi-process Rx and Tx")
Cc: stable@dpdk.org
Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>