Ping: Add TTL config option and value to output

[Optimoos]

This change adds the TTL value of the inbound packet to the output of the userland ping program, bringing it more in line with other common ping utilities. It also adds the (optional) -t option to configure the TTL of the outgoing packet if desired.

[Optimoos]

As an aside, this took me way longer to sort out that it should have because QEMU's "SLIRP" networking was creating havoc with the TTL values, at least for me under Windows. Changing to a tap interface resolved this, and I don't have a Linux machine handy at the moment to see if the issue is repeated there.

[Optimoos]

Thanks for the feedback Jelle, I've made some adjustments.