examples/l2fwd-cat: make build dependent on pqos lib
examples/l2fwd-cat: make build dependent on pqos lib

The l2fwd-cat example uses the pqos library to work, so make the meson
build dependent on the presence of that library

Signed-off-by: Bruce Richardson <66b9e8e8fbd5e9f41f91b0af050876182ce9d0e4@intel.com>
Tested-by: Harry van Haaren <b9ad04ed670c22cfa7f5f9ab17e311ca85d11a76@intel.com>

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