ieee802154: add definitions for link-layer security and header functions

When dealing with 802.15.4, one often has to know the maximum payload
size for a given packet. This depends on many factors, one of which is
whether or not a security header is present in the frame. These
definitions and functions provide an easy way for any upper layer to
calculate the maximum payload size for a packet. The first obvious user
for this is 6lowpan, which duplicates this calculation and gets it
partially wrong because it ignores security headers.

Signed-off-by: Phoebe Buckheister <phoebe.buckheister@itwm.fraunhofer.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/ieee802154.h b/include/net/ieee802154.h
index c7ae0ac..0aa7122 100644
--- a/include/net/ieee802154.h
+++ b/include/net/ieee802154.h
@@ -79,6 +79,15 @@
 #define IEEE802154_SCF_KEY_SHORT_INDEX		2
 #define IEEE802154_SCF_KEY_HW_INDEX		3
 
+#define IEEE802154_SCF_SECLEVEL_NONE		0
+#define IEEE802154_SCF_SECLEVEL_MIC32		1
+#define IEEE802154_SCF_SECLEVEL_MIC64		2
+#define IEEE802154_SCF_SECLEVEL_MIC128		3
+#define IEEE802154_SCF_SECLEVEL_ENC		4
+#define IEEE802154_SCF_SECLEVEL_ENC_MIC32	5
+#define IEEE802154_SCF_SECLEVEL_ENC_MIC64	6
+#define IEEE802154_SCF_SECLEVEL_ENC_MIC128	7
+
 /* MAC footer size */
 #define IEEE802154_MFR_SIZE	2 /* 2 octets */