nfp: disallow sharing mutexes on the same machine

NFP can be connected to multiple machines via PCI or other buses.
Access to hardware resources is arbitrated using locks residing
in device memory.  Currently nfpcore only respects the mutexes
when it comes to inter-host locking, but if we try to acquire
the same lock again, on one host - it will simply return success
because owner of the lock is already set to that host.

This makes the locks useless for arbitration within one host
and unfair because whichever host grabbed the lock will have
a chance to reacquire it without others getting a shot.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/netronome/nfp/nfpcore/nfp_cppcore.c

@@ -1736,11 +1736,5 @@ int nfp_cpp_mutex_trylock(struct nfp_cpp_mutex *mutex)
 		return 0;
 	}
 
-	/* Already locked by us? Success! */
-	if (tmp == value) {
-		mutex->depth = 1;
-		return 0;
-	}
-
 	return nfp_mutex_is_locked(tmp) ? -EBUSY : -EINVAL;
 }