[mod_extforward] support longer PROXY v2 TLV vec

support longer HAProxy PROXY protocol v2 TLV vector
(allow up to 2k total for header + TLVs, saved on stack,
 and expecting <= MTU size (typically 1536 bytes))

src/mod_extforward.c

@@ -1255,6 +1255,7 @@ union hap_PROXY_hdr {
             } unx;
         } addr;
     } v2;
+    uint64_t ext[32]; /* 2k (- hdr) for v2 TLV extensions (at least 1536 MTU) */
 };
 
 /*