Basic implementation of TCP over XDP for Knot server

including connection handling for kxdpgun in TCP mode.

The implementation is not perfect!! But the interface with other Knot parts is stable.

src/contrib/dynarray.h

@@ -50,7 +50,7 @@
 	} prefix ## _dynarray_t; \
 	\
 	visibility ntype *prefix ## _dynarray_arr(prefix ## _dynarray_t *dynarray); \
-	visibility void prefix ## _dynarray_add(prefix ## _dynarray_t *dynarray, \
+	visibility ntype *prefix ## _dynarray_add(prefix ## _dynarray_t *dynarray, \
 	                                        ntype const *to_add); \
 	visibility void prefix ## _dynarray_free(prefix ## _dynarray_t *dynarray);
 
@@ -88,11 +88,11 @@
 	} \
 	\
 	_unused_ \
-	visibility void prefix ## _dynarray_add(struct prefix ## _dynarray *dynarray, \
-	                                        ntype const *to_add) \
+	visibility ntype *prefix ## _dynarray_add(struct prefix ## _dynarray *dynarray, \
+	                                          ntype const *to_add) \
 	{ \
 		if (dynarray->capacity < 0) { \
-			return; \
+			return NULL; \
 		} \
 		if (dynarray->capacity == 0) { \
 			dynarray->capacity = sizeof(dynarray->init) / sizeof(*dynarray->init); \
@@ -104,7 +104,7 @@
 			if (new_arr == NULL) { \
 				prefix ## _dynarray_free__(dynarray); \
 				dynarray->capacity = dynarray->size = -1; \
-				return; \
+				return NULL; \
 			} \
 			if (dynarray->capacity > 0) { \
 				memcpy(new_arr, prefix ## _dynarray_arr(dynarray), \
@@ -115,7 +115,9 @@
 			dynarray->capacity = new_capacity; \
 			dynarray->arr = prefix ## _dynarray_arr_arr__; \
 		} \
-		prefix ## _dynarray_arr(dynarray)[dynarray->size++] = *to_add; \
+		ntype *add_to = &prefix ## _dynarray_arr(dynarray)[dynarray->size++]; \
+		*add_to = *to_add; \
+		return add_to; \
 	} \
 	\
 	_unused_ \