netlabel: Add functionality to set the security attributes of a packet

This patch builds upon the new NetLabel address selector functionality by
providing the NetLabel KAPI and CIPSO engine support needed to enable the
new packet-based labeling.  The only new addition to the NetLabel KAPI at
this point is shown below:

 * int netlbl_skbuff_setattr(skb, family, secattr)

... and is designed to be called from a Netfilter hook after the packet's
IP header has been populated such as in the FORWARD or LOCAL_OUT hooks.

This patch also provides the necessary SELinux hooks to support this new
functionality.  Smack support is not currently included due to uncertainty
regarding the permissions needed to expand the Smack network access controls.

Signed-off-by: Paul Moore <paul.moore@hp.com>
Reviewed-by: James Morris <jmorris@namei.org>
diff --git a/include/net/netlabel.h b/include/net/netlabel.h
index 0729f8c..3f67e6d 100644
--- a/include/net/netlabel.h
+++ b/include/net/netlabel.h
@@ -382,6 +382,9 @@
 			const struct netlbl_lsm_secattr *secattr);
 int netlbl_sock_getattr(struct sock *sk,
 			struct netlbl_lsm_secattr *secattr);
+int netlbl_skbuff_setattr(struct sk_buff *skb,
+			  u16 family,
+			  const struct netlbl_lsm_secattr *secattr);
 int netlbl_skbuff_getattr(const struct sk_buff *skb,
 			  u16 family,
 			  struct netlbl_lsm_secattr *secattr);
@@ -451,6 +454,12 @@
 {
 	return -ENOSYS;
 }
+static inline int netlbl_skbuff_setattr(struct sk_buff *skb,
+				      u16 family,
+				      const struct netlbl_lsm_secattr *secattr)
+{
+	return -ENOSYS;
+}
 static inline int netlbl_skbuff_getattr(const struct sk_buff *skb,
 					u16 family,
 					struct netlbl_lsm_secattr *secattr)