vtnet tcp LRO init is done conditionally, depending on the `vtnet_software_lro()` return value.
In some cases it returns false, resulting in empty lro_ctl being present in the rxq.
Thus, on receipt of the first packet, kernel panics when trying to set curvnet from the lro_ctl->ifp.
```
#15 0xffffffff810cb49b in trap (frame=0xfffffe00639fa7d0) at /usr/home/melifaro/free/head/sys/amd64/amd64/trap.c:398
#16 <signal handler called>
#17 0xffffffff80df1b24 in tcp_lro_flush_all (lc=lc@entry=0xfffff8000382bca8) at /usr/home/melifaro/free/head/sys/netinet/tcp_lro.c:1442
#18 0xffffffff80a4ef7a in vtnet_rxq_eof (rxq=<optimized out>, rxq@entry=0xfffff8000382bc00) at /usr/home/melifaro/free/head/sys/dev/virtio/network/if_vtnet.c:2148
#19 0xffffffff80a4e5d7 in vtnet_rx_vq_process (rxq=0xfffff8000382bc00, tries=<optimized out>) at /usr/home/melifaro/free/head/sys/dev/virtio/network/if_vtnet.c:2207
#20 0xffffffff80c748da in taskqueue_run_locked (queue=queue@entry=0xfffff800037b3600) at /usr/home/melifaro/free/head/sys/kern/subr_taskqueue.c:476
#21 0xffffffff80c75964 in taskqueue_thread_loop (arg=arg@entry=0xfffff8000382bc80) at /usr/home/melifaro/free/head/sys/kern/subr_taskqueue.c:793
#22 0xffffffff80bcc8a0 in fork_exit (callout=0xffffffff80c758d0 <taskqueue_thread_loop>, arg=0xfffff8000382bc80, frame=0xfffffe00639fab00) at /usr/home/melifaro/free/head/sys/kern/kern_fork.c:1078
#23 <signal handler called>
(kgdb) up 17
#17 0xffffffff80df1b24 in tcp_lro_flush_all (lc=lc@entry=0xfffff8000382bca8) at /usr/home/melifaro/free/head/sys/netinet/tcp_lro.c:1442
1442 CURVNET_SET(lc->ifp->if_vnet);
(kgdb) p lc
$1 = (struct lro_ctrl *) 0xfffff8000382bca8
(kgdb) p lc->ifp
$2 = (struct ifnet *) 0x0
(kgdb) p *lc
$3 = {ifp = 0x0, lro_mbuf_data = 0x0, lro_last_queue_time = 0, lro_queued = 0, lro_flushed = 0, lro_bad_csum = 0, lro_cnt = 0, lro_mbuf_count = 0, lro_mbuf_max = 0, lro_ackcnt_lim = 0,
lro_length_lim = 0, lro_hashsz = 0, lro_hash = 0x0, lro_active = {lh_first = 0x0}, lro_free = {lh_first = 0x0}}
```