mac80211: skip encap offload for tx multicast/control packets

This simplifies the checks in the encap offload tx handler and allows using
it in cases where software crypto is used for multicast packets, e.g. when
using an AP_VLAN.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20200908123702.88454-4-nbd@nbd.name


Signed-off-by: Johannes Berg <johannes.berg@intel.com>