net/bonding: fix RSS with early configure

net/bonding: fix RSS with early configure

RSS don't work when bond_ethdev_configure called before
rte_eth_bond_slave_add.

This is because internals->rss_key_len is 0 in bond_ethdev_configure().
If internals->rss_key_len is 0, internals->rss_key can not be set
properly.

e.g.:
doesn't work (examples/bond/main.c):
rte_eth_bond_create()
rte_eth_dev_configure()
rte_eth_bond_slave_add()
rte_eth_dev_start()

works (testpmd):
rte_eth_bond_create()
rte_eth_bond_slave_add()
rte_eth_dev_configure()
rte_eth_dev_start()

Fixing by using 'default_rss_key' when 'internals->rss_key_len' is 0.

Fixes: 6b1a001ec546 ("net/bonding: fix RSS key length")
Cc: stable@dpdk.org
Signed-off-by: Yu Wenjun <yuwenjun@cmss.chinamobile.com>
Acked-by: Min Hu (Connor) <humin29@huawei.com>