mctp: Add MCTP base

Add basic Kconfig, an initial (empty) af_mctp source object, and
{AF,PF}_MCTP definitions, and the required definitions for a new
protocol type.

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/Kconfig b/net/Kconfig
index c7392c4..fb13460 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -363,6 +363,7 @@
 source "net/rxrpc/Kconfig"
 source "net/kcm/Kconfig"
 source "net/strparser/Kconfig"
+source "net/mctp/Kconfig"
 
 config FIB_RULES
 	bool