strip the prefix from ipv4-mapped addresses

This allows to have plain IPv4 addresses in log, even if listening
on an IPv6 socket.

Before:

    ::ffff:10.7.7.72 - - [24/Jan/2025:22:15:54 +0100] "GET /archive.tar.zst HTTP/1.1" 200 72194 "" "pacredir/0.4.8 (arch/x86_64)"

After:

    10.7.7.72 - - [24/Jan/2025:22:15:54 +0100] "GET /archive.tar.zst HTTP/1.1" 200 72194 "" "pacredir/0.4.8 (arch/x86_64)"

darkhttpd.c

@@ -799,6 +799,10 @@ static const char *get_address_text(const void *addr) {
         static char text_addr[INET6_ADDRSTRLEN];
         const struct in6_addr *in6_addr = addr;
         inet_ntop(AF_INET6, in6_addr, text_addr, INET6_ADDRSTRLEN);
+        /* IPv4 addresses via dual stack result in mapped IPv6 addresses.
+           Strip the prefix (::ffff:) for plain IPv4 addresses. */
+        if (IN6_IS_ADDR_V4MAPPED(in6_addr))
+            return text_addr + 7;
         return text_addr;
     } else
 #endif