Fix bug in patty_ax25_if_addr_add()

Fix bug in patty_ax25_if_addr_add() wherein, due to a typo of memcpy()
rather than memcmp(), the function would never fail to add an address
to an interface, even if it already exists on the interface

src/if.c

@@ -165,7 +165,7 @@ static patty_ax25_addr *find_addr(patty_ax25_if *iface,
     while (item) {
         patty_ax25_addr *cur = item->value;
 
-        if (memcpy(&addr->callsign,
+        if (memcmp(&addr->callsign,
                    &cur->callsign,
                    sizeof(addr->callsign)) == 0) {
             return addr;