mctp: replace mctp_address_ok with more fine-grained helpers

Currently, we have mctp_address_ok(), which checks if an EID is in the
"valid" range of 8-254 inclusive. However, 0 and 255 may also be valid
addresses, depending on context. 0 is the NULL EID, which may be set
when physical addressing is used. 255 is valid as a destination address
for broadcasts.

This change renames mctp_address_ok to mctp_address_unicast, and adds
similar helpers for broadcast and null EIDs, which will be used in an
upcoming commit.

Signed-off-by: Jeremy Kerr <[e-mail]>
Signed-off-by: Jakub Kicinski <[e-mail]>

include/net/mctp.h

···
 
 #define MCTP_INITIAL_DEFAULT_NET	1
 
-static inline bool mctp_address_ok(mctp_eid_t eid)
+static inline bool mctp_address_unicast(mctp_eid_t eid)
 {
 	return eid >= 8 && eid < 255;
+}
+
+static inline bool mctp_address_broadcast(mctp_eid_t eid)
+{
+	return eid == 255;
+}
+
+static inline bool mctp_address_null(mctp_eid_t eid)
+{
+	return eid == 0;
 }
 
 static inline bool mctp_address_matches(mctp_eid_t match, mctp_eid_t eid)

net/mctp/device.c

···
 	if (!mdev)
 		return -ENODEV;
 
-	if (!mctp_address_ok(addr->s_addr))
+	if (!mctp_address_unicast(addr->s_addr))
 		return -EINVAL;
 
 	/* Prevent duplicates. Under RTNL so don't need to lock for reading */

net/mctp/neigh.c

···
 	}
 
 	eid = nla_get_u8(tb[NDA_DST]);
-	if (!mctp_address_ok(eid)) {
+	if (!mctp_address_unicast(eid)) {
 		NL_SET_ERR_MSG(extack, "Invalid neighbour EID");
 		return -EINVAL;
 	}

net/mctp/route.c

···
 	struct net *net = dev_net(mdev->dev);
 	struct mctp_route *rt, *ert;
 
-	if (!mctp_address_ok(daddr_start))
+	if (!mctp_address_unicast(daddr_start))
 		return -EINVAL;
 
 	if (daddr_extent > 0xff || daddr_start + daddr_extent >= 255)