devtools: add cocci script to rename mbuf offload flags

The mbuf offload flags do not match the DPDK namespace (they are not
prefixed by RTE_). This coccinelle script is used in the next commit to
do the replacement in the code.

A draft script was initially submitted [1] in commit d7595795b760 ("doc:
announce renaming of mbuf offload flags"), but dropped by mistake at
commit.

1: http://inbox.dpdk.org/dev/20210730155700.32574-1-olivier.matz@6wind.com

Signed-off-by: Olivier Matz <olivier.matz@6wind.com>