net: pkt: Add helper function to initialize TX packet

Add helper function to initialize externally allocated TX packet. It's
especially important to configure net_buf slab for the packet so that
net buffers are allocated from a correct pool for the packet.

Signed-off-by: Robert Lubos <[email protected]>
(cherry picked from commit b8c7984)

Author: rlubos

subsys/net/ip/net_pkt.c

@@ -2354,6 +2354,19 @@ int net_pkt_set_data(struct net_pkt *pkt,
 	return net_pkt_write(pkt, access->data, access->size);
 }
 
+void net_pkt_tx_init(struct net_pkt *pkt)
+{
+	memset(pkt, 0, sizeof(struct net_pkt));
+
+	pkt->atomic_ref = ATOMIC_INIT(1);
+	pkt->slab = &tx_pkts;
+
+	net_pkt_set_ipv6_next_hdr(pkt, 255);
+	net_pkt_set_priority(pkt, TX_DEFAULT_PRIORITY);
+	net_pkt_set_vlan_tag(pkt, NET_VLAN_TAG_UNSPEC);
+	net_pkt_cursor_init(pkt);
+}
+
 void net_pkt_init(void)
 {
 #if CONFIG_NET_PKT_LOG_LEVEL >= LOG_LEVEL_DBG

subsys/net/ip/net_private.h

@@ -414,3 +414,10 @@ static inline void net_pkt_print_buffer_info(struct net_pkt *pkt, const char *st
 
 	printk("\n");
 }
+
+/**
+ * Initialize externally allocated TX packet.
+ *
+ * @param pkt The network packet to initialize.
+ */
+void net_pkt_tx_init(struct net_pkt *pkt);