examples/l2fwd-crypto: fix build with pkg-config

examples/l2fwd-crypto: fix build with pkg-config

Two issues fixed here.

First add the experimental flag.
Then fix a link issue with the crypto scheduler driver:
/usr/bin/ld: /tmp/cchr7aHA.o: in function `main':
main.c:(.text.startup+0x1673): undefined reference to
`rte_cryptodev_scheduler_workers_get'
collect2: error: ld returned 1 exit status

Fixes: e3bcb99a5e13 ("examples/l2fwd-crypto: limit number of sessions")
Fixes: 261bbff75e34 ("examples: use separate crypto session mempools")
Cc: stable@dpdk.org
Signed-off-by: David Marchand <david.marchand@redhat.com>