net/enic: set rte errno to positive value
net/enic: set rte errno to positive value

Related to d9fff8a31, where rte_errno should always have positive
errno values.

Technically this is an ABI change since it fixes an error code
introduced in 18.02, but is minor and inconsequential.

Fixes: 1e81dbb5321b ("net/enic: add Tx prepare handler")
Cc: stable@dpdk.org

Signed-off-by: Hyong Youb Kim <410cadac1eb3154f1b3752aedc2559ad69f3863e@cisco.com>
Reviewed-by: John Daley <097981eb5abe5dbeac3142a4f5a88742d916de86@cisco.com>
Reviewed-by: Aaron Conole <aa17ba42a0685b214660ffb377dc7569a94d48c9@redhat.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk