debugnet: Add ifnet accessor to set debugnet methods

As part of the effort to hide the internals of the ifnet struct, convert
the DEBUGNET_SET() macro to use an accessor instead of directly touching
the methods member.

Reviewed by:	glebius (older version)
Sponsored by:	Juniper Networks, Inc.
Differential Revision: https://reviews.freebsd.org/D38105

sys/net/debugnet.h

@@ -263,7 +263,7 @@ extern int debugnet_arp_nretries;
 #define	DEBUGNET_NOTIFY_MTU(ifp)	debugnet_any_ifnet_update(ifp)
 
 #define	DEBUGNET_SET(ifp, driver)				\
-	(ifp)->if_debugnet_methods = &driver##_debugnet_methods
+	if_setdebugnet_methods((ifp), &driver##_debugnet_methods)
 
 #else /* !DEBUGNET || !INET */
 

sys/net/if.c

@@ -4803,6 +4803,12 @@ if_setgetcounterfn(if_t ifp, if_get_counter_t fn)
 	ifp->if_get_counter = fn;
 }
 
+void
+if_setdebugnet_methods(if_t ifp, struct debugnet_methods *m)
+{
+	ifp->if_debugnet_methods = m;
+}
+
 #ifdef DDB
 static void
 if_show_ifnet(struct ifnet *ifp)

sys/net/if_var.h

@@ -653,6 +653,7 @@ void if_settransmitfn(if_t ifp, if_transmit_fn_t);
 void if_setqflushfn(if_t ifp, if_qflush_fn_t);
 void if_setgetcounterfn(if_t ifp, if_get_counter_t);
 void if_setsndtagallocfn(if_t ifp, if_snd_tag_alloc_t);
+void if_setdebugnet_methods(struct ifnet *, struct debugnet_methods *);
 
 /* TSO */
 void if_hw_tsomax_common(if_t ifp, struct ifnet_hw_tsomax *);