Fixes this error in the configure-time test for "Linux PF_PACKET sockets":

test.c:7:11: error: function definition is not allowed here
    7 | int foo() { return ETH_P_ALL; }
      |           ^
1 error generated.

Which changes this configure log message:
checking for Linux PF_PACKET sockets... no

to this:
checking for Linux PF_PACKET sockets... yes

which fixes this error in the command 'sudo nping --arp 192.168.12.1':

doArp: failed to open device wlan0

--- a/libdnet-stripped/configure
+++ b/libdnet-stripped/configure
@@ -15116,10 +15116,10 @@ printf %s "checking for Linux PF_PACKET sockets... " >&6; }
 /* end confdefs.h.  */
 #include <netpacket/packet.h>
                     #include <linux/if_ether.h>
+int foo() { return ETH_P_ALL; }
 int
 main (void)
 {
-int foo() { return ETH_P_ALL; }
   ;
   return 0;
 }
