net/ionic: revise configuration flag handling

net/ionic: revise configuration flag handling

Configuration flags come to the driver in dev_configure(). From there,
the driver calls ionic_lif_configure() to update the lif->feature
bitfield, and then programs the port.

Features like VLAN_RX_FILTER and RX_HASH cannot be disabled in the
device, so do nothing in response to requests to disable them. (The
device config would ideally show them enabled by default, but some
DTS tests fail if RSS_HASH is set but RSS is not.)

Move features from the per-queue to per-port lists. IONIC does not
really support per-queue configuration: the stack disallows disabling
a queue feature if it is enabled on the port, while the device
disallows enabling a queue feature if it is disabled on the port.
Thus all configuration is per-port.

Move the guts of ionic_vlan_offload_set() into a new function,
ionic_lif_configure_vlan_offload(), so it can be called by
ionic_lif_configure().

Move the check for DEV_RX_OFFLOAD_SCATTER from rx_queue_setup() up
into ionic_lif_configure().

Warn if rx_drop_en is not set.

Signed-off-by: Andrew Boyer <aboyer@pensando.io>