respond/reject: guard Ethernet setup against non-Ethernet packets

When running with --reject-dev in autofp mode, the libnet context is
cached thread-locally and t_inject_mode is latched to LIBNET_LINK on the
first reject for an Ethernet packet. Subsequent rejects from different
interfaces that hit the fast path reuse the cached ctx but incorrectly
still call SetupEthernet(), which dereferences PacketGetEthernet() causing
a crash.

To address this check for if a packet is ethernet in all entry points.

Ticket: #8832.

src/respond-reject-libnet11.c

@@ -249,6 +249,8 @@ static inline int BuildIPv6(libnet_t *c, Libnet11Packet *lpacket, const uint8_t
 
 static inline void SetupEthernet(Packet *p, Libnet11Packet *lpacket, enum RejectDirection dir)
 {
+    if (!PacketIsEthernet(p))
+        return;
     const EthernetHdr *ethh = PacketGetEthernet(p);
     switch (dir) {
         case REJECT_DIR_SRC:
@@ -328,7 +330,7 @@ int RejectSendLibnet11IPv4TCP(ThreadVars *tv, Packet *p, void *data, enum Reject
     if (BuildIPv4(c, &lpacket, IPPROTO_TCP) < 0)
         goto cleanup;
 
-    if (t_inject_mode == LIBNET_LINK) {
+    if (t_inject_mode == LIBNET_LINK && PacketIsEthernet(p)) {
         SetupEthernet(p, &lpacket, dir);
 
         if (p->vlan_idx == 1) {
@@ -405,7 +407,7 @@ int RejectSendLibnet11IPv4ICMP(ThreadVars *tv, Packet *p, void *data, enum Rejec
     if (BuildIPv4(c, &lpacket, IPPROTO_ICMP) < 0)
         goto cleanup;
 
-    if (t_inject_mode == LIBNET_LINK) {
+    if (t_inject_mode == LIBNET_LINK && PacketIsEthernet(p)) {
         SetupEthernet(p, &lpacket, dir);
 
         if (p->vlan_idx == 1) {
@@ -470,7 +472,7 @@ int RejectSendLibnet11IPv6TCP(ThreadVars *tv, Packet *p, void *data, enum Reject
     if (BuildIPv6(c, &lpacket, IPPROTO_TCP) < 0)
         goto cleanup;
 
-    if (t_inject_mode == LIBNET_LINK) {
+    if (t_inject_mode == LIBNET_LINK && PacketIsEthernet(p)) {
         SetupEthernet(p, &lpacket, dir);
         if (p->vlan_idx == 1) {
             if (BuildEthernetVLAN(c, &lpacket, ETHERNET_TYPE_IPV6, p->vlan_id[0]) < 0)
@@ -547,7 +549,7 @@ int RejectSendLibnet11IPv6ICMP(ThreadVars *tv, Packet *p, void *data, enum Rejec
     if (BuildIPv6(c, &lpacket, IPPROTO_ICMPV6) < 0)
         goto cleanup;
 
-    if (t_inject_mode == LIBNET_LINK) {
+    if (t_inject_mode == LIBNET_LINK && PacketIsEthernet(p)) {
         SetupEthernet(p, &lpacket, dir);
         if (p->vlan_idx == 1) {
             if (BuildEthernetVLAN(c, &lpacket, ETHERNET_TYPE_IPV6, p->vlan_id[0]) < 0)