# iftop -i eth0
interface: eth0
pcap_open_live(eth0): eth0: socket: Address family not supported by protocol
# dmesg | tail
[595841.213279] iftop uses obsolete (PF_INET,SOCK_PACKET)

Make sure that CONFIG_PACKET and CONFIG_PACKET_DIAG are enabled in your kernel config

$ diff .config.old .config
3c3
< # Linux/x86 4.4.70 Kernel Configuration
---
> # Linux/x86 4.4.89 Kernel Configuration
635c635,636
< # CONFIG_PACKET is not set
---
> CONFIG_PACKET=m
> CONFIG_PACKET_DIAG=m
$