iflib handled no RSS ioctl, so SIOCGIFRSSKEY and SIOCGIFRSSHASH reached
ether_ioctl() and returned EINVAL for every iflib driver.
Add ifdi_rss_key_get, ifdi_rss_key_set, ifdi_rss_hash_get,
ifdi_rss_table_get and ifdi_rss_table_set, following ifdi_i2c_req: a
generic ioctl behind a driver method defaulting to ENOTSUP. Methods
sharing a signature share one default.
isc_rss_table_size is the authority for the table length, since iflib
already masks flowids with it in QIDX(). Gets clear the caller's buffer
past the interface name.
Signed-off-by: Nick Price <nprice@FreeBSD.org>