app/regex: fix mbuf size for multi-segment buffer

app/regex: fix mbuf size for multi-segment buffer

When allocating multi segmented buffers, and in case there is
a remainder in total buf len, the actual job len might be more
than expected job_len.

This adds additional space in the mbuf in the multi seg case,
to allow the remaining memory to be stored in one segment.

Fixes: c1d1b94eec58 ("app/regex: fix number of matches")
Cc: stable@dpdk.org
Signed-off-by: Raslan Darawsheh <rasland@nvidia.com>
Acked-by: Ori Kam <orika@nvidia.com>