lib/osutil: Fix raising max FDs on macOS (#7507)

There was a logic mistake, so the limit in question wasn't used. On my
macOS this doesn't seem to matter, the hard limit returned is 2^63-1 and
setting the soft limit to that works. However I'm assuming that's not
the case for older macOSes since it was so nicely documented, so we
should still have this working. (10240 FDs should be enough for
anybody.)

lib/osutil/rlimit_unix.go

@@ -36,7 +36,7 @@ func MaximizeOpenFileLimit() (int, error) {
 	// macOS doesn't like a soft limit greater then OPEN_MAX
 	// See also: man setrlimit
 	if runtime.GOOS == "darwin" && lim.Max > darwinOpenMax {
-		lim.Cur = darwinOpenMax
+		lim.Max = darwinOpenMax
 	}
 
 	// Try to increase the limit to the max.