ci: update Meson option for generic build

ci: update Meson option for generic build

The way we're building DPDK in CI, with -Dmachine=default, has not been
updated when the option got replaced to preserve a backwards-complatible
build call to facilitate ABI verification between DPDK versions. Update
the call to use -Dplatform=generic, which is the most up to date way to
execute the same build which is now present in all DPDK versions the ABI
check verifies.

Signed-off-by: Juraj Linkeš <juraj.linkes@pantheon.tech>
Acked-by: Aaron Conole <aconole@redhat.com>