#include <stdio.h>
#include <net/if.h>
#include <net/pfvar.h>

int main (void) {
	printf("%zu\n", sizeof(struct pfioc_rule));
}

Index: sshuttle/methods/pf.py
--- sshuttle/methods/pf.py.orig
+++ sshuttle/methods/pf.py
@@ -266,7 +266,7 @@ class OpenBsd(Generic):
                         ("proto_variant", c_uint8),
                         ("direction", c_uint8)]
 
-        self.pfioc_rule = c_char * 3424
+        self.pfioc_rule = c_char * 3408
         self.pfioc_natlook = pfioc_natlook
         super(OpenBsd, self).__init__()