Cannot run hping3 against a host on remote VPN link - Issue with too many interfaces - VPN link on my laptop is #48 - hping3 stops searching after 16 interfaces

It appears that I cannot get `hping3` to ping a host in a remote network when connected via VPN tunnel. I'm not sure whether the issue is that I have too many interfaces (I do lots of virtualization on my laptop and currently have 48 interfaces - mainly due to LXD containers).

I've tried forcing which interface to use via the `-I tun0` flag but no joy - `hping3` always binds to `lo` for hosts on the remote subnet.

List of interfaces (too many to list here - unless explicitly requested):
```
$ ip l l | awk '/^[0-9]*:/ {print}'| wc -l
48
```
Routing info (relevant route listed):
```
$ ip r l | egrep 10.2.20
10.2.20.0/24 via 10.64.192.14 dev tun0
```
Route to remote host:
```
[Fri Jul 27 17:33:31 - 4.15.0-29-generic - /dev/pts/26]
[akk@akk-m6700 10.0.0.13: ~/source/hping (master)]
$ ip r g 10.2.20.74
10.2.20.74 via 10.64.192.14 dev tun0 src 10.64.192.13
cache
```
Attempt to hping:
```
[Fri Jul 27 17:29:06 - 4.15.0-29-generic - /dev/pts/26]
[akk@akk-m6700 10.0.0.13: ~/source/hping (master)]
$ sudo ./hping3 -I tun0 -S -p 443 10.2.20.74
HPING 10.2.20.74 (lo 10.2.20.74): S set, 40 headers + 0 data bytes
^C
--- 10.2.20.74 hping statistic ---
5 packets tramitted, 0 packets received, 100% packet loss
round-trip min/avg/max = 0.0/0.0/0.0 ms
```
A simple ping:
```
[Fri Jul 27 17:31:32 - 4.15.0-29-generic - /dev/pts/26]
[akk@akk-m6700 10.0.0.13: ~/source/hping (master)]
$ ping -c4 10.2.20.74
PING 10.2.20.74 (10.2.20.74) 56(84) bytes of data.
From 10.64.192.222: icmp_seq=1 Redirect Network(New nexthop: 10.64.192.211)
64 bytes from 10.2.20.74: icmp_seq=1 ttl=62 time=12.1 ms
From 10.64.192.222: icmp_seq=2 Redirect Network(New nexthop: 10.64.192.211)
64 bytes from 10.2.20.74: icmp_seq=2 ttl=62 time=12.5 ms
From 10.64.192.222: icmp_seq=3 Redirect Network(New nexthop: 10.64.192.211)
64 bytes from 10.2.20.74: icmp_seq=3 ttl=62 time=13.0 ms
From 10.64.192.222: icmp_seq=4 Redirect Network(New nexthop: 10.64.192.211)
64 bytes from 10.2.20.74: icmp_seq=4 ttl=62 time=11.6 ms

--- 10.2.20.74 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3003ms
rtt min/avg/max/mdev = 11.670/12.542/13.082/0.436 ms
```

Let me know what else to provide to help narrow the problem.