net: ieee802154: return -EINVAL for unknown addr type

This patch adds handling to return -EINVAL for an unknown addr type. The
current behaviour is to return 0 as successful but the size of an
unknown addr type is not defined and should return an error like -EINVAL.

Fixes: 94160108

 ("net/ieee802154: fix uninit value bug in dgram_sendmsg")
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>