iflib: invert default restart on VLAN changes

In rS360398, a new iflib device method was added to opt out of VLAN
events needing an interface reset.

I am switching the default to not requiring a restart for:
* VLAN events
* unknown events

After fixing various bugs, I do not think this would be a common need
of hardware and it is undesirable from the user's perspective causing
link flaps and much slower VLAN configuration. Currently, there are no
other restart events besides VLAN events, and setting the
ifdi_needs_restart default to false will alleviate the need to churn
every driver if an odd event is added in the future for specific
hardware.

markj points out this could cause churn in the other direction; I will
solve that problem with an event registration system as he mentions in
the review should we need it in the future.

These drivers will opt into restart and need further inspection or work:
* ixv (needs code audit, 61a8231 fixed principal issue; re-init probably
not necessary)
* axgbe (needs code audit; re-init probably not necessary)
* iavf - (needs code audit; interaction with Malicious Driver Detection
mentioned in rS360398)
* mgb - no VLAN functions are currently implemented. Left a comment.

MFC after:	2 weeks
Sponsored by:	BBOX.io
Differential Revision:	https://reviews.freebsd.org/D41558

sys/dev/e1000/if_em.c

@@ -4383,7 +4383,7 @@ em_if_get_counter(if_ctx_t ctx, ift_counter cnt)
  * @ctx: iflib context
  * @event: event code to check
  *
- * Defaults to returning true for unknown events.
+ * Defaults to returning false for unknown events.
  *
  * @returns true if iflib needs to reinit the interface
  */
@@ -4392,9 +4392,8 @@ em_if_needs_restart(if_ctx_t ctx __unused, enum iflib_restart_event event)
 {
 	switch (event) {
 	case IFLIB_RESTART_VLAN_CONFIG:
-		return (false);
 	default:
-		return (true);
+		return (false);
 	}
 }
 

sys/dev/igc/if_igc.c

@@ -2402,7 +2402,7 @@ igc_if_get_counter(if_ctx_t ctx, ift_counter cnt)
  * @ctx: iflib context
  * @event: event code to check
  *
- * Defaults to returning true for unknown events.
+ * Defaults to returning false for unknown events.
  *
  * @returns true if iflib needs to reinit the interface
  */
@@ -2411,9 +2411,8 @@ igc_if_needs_restart(if_ctx_t ctx __unused, enum iflib_restart_event event)
 {
 	switch (event) {
 	case IFLIB_RESTART_VLAN_CONFIG:
-		return (false);
 	default:
-		return (true);
+		return (false);
 	}
 }
 

sys/dev/ixgbe/if_ix.c

@@ -1256,7 +1256,7 @@ ixgbe_if_i2c_req(if_ctx_t ctx, struct ifi2creq *req)
  * @ctx: iflib context
  * @event: event code to check
  *
- * Defaults to returning true for unknown events.
+ * Defaults to returning false for unknown events.
  *
  * @returns true if iflib needs to reinit the interface
  */
@@ -1265,9 +1265,8 @@ ixgbe_if_needs_restart(if_ctx_t ctx __unused, enum iflib_restart_event event)
 {
 	switch (event) {
 	case IFLIB_RESTART_VLAN_CONFIG:
-		return (false);
 	default:
-		return (true);
+		return (false);
 	}
 }
 

sys/dev/mgb/if_mgb.c

@@ -251,6 +251,7 @@ static device_method_t mgb_iflib_methods[] = {
 	 */
 	DEVMETHOD(ifdi_vlan_register, mgb_vlan_register),
 	DEVMETHOD(ifdi_vlan_unregister, mgb_vlan_unregister),
+	DEVMETHOD(ifdi_needs_restart, mgb_if_needs_restart),
 
 	/*
 	 * Needed for WOL support

sys/net/ifdi_if.m

@@ -115,7 +115,7 @@ CODE {
 	static bool
 	null_needs_restart(if_ctx_t _ctx __unused, enum iflib_restart_event _event __unused)
 	{
-		return (true);
+		return (false);
 	}
 };