ping(8): Manual page cleanup and fixes

[jlduran]

This Pull Request is divided in three commits:

1. Appease mandoc and igor.
2. Use example.com instead of foo.com.
3. Update the IPv4 TTL section specifically for FreeBSD and remove old references.

[gbergling]

The man page review is fine from my perspective. Can't speak for the TTL updates to the man page. I would create a differential for it, for the TTL updates.

[jlduran]

Thank you!

I wonder if it helps, to visually understand the proposed change:

ping -4 -c1 www.freebsd.org
PING wfe2.nyi.freebsd.org (96.47.72.95): 56 data bytes
64 bytes from 96.47.72.95: icmp_seq=0 ttl=<64 - number of routers in the path> time=0.001 ms

--- wfe2.nyi.freebsd.org ping statistics ---
1 packets transmitted, 1 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 0.001/0.001/0.001/0.000 ms

Explanation:
The target system is FreeBSD (with net.inet.ip.ttl=64, the default). If you try to ping a target that uses 255, for example, OpenBSD:

ping -4 -c1 www.openbsd.org
PING www.openbsd.org (199.185.178.80): 56 data bytes
64 bytes from 199.185.178.80: icmp_seq=0 ttl=<255 - number of routers in the path> time=0.001 ms

--- www.openbsd.org ping statistics ---
1 packets transmitted, 1 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 0.001/0.001/0.001/0.000 ms

Or Windows (128):

ping -4 -c1 live.com
PING live.com (204.79.197.212): 56 data bytes
64 bytes from 204.79.197.212: icmp_seq=0 ttl=<128 - number of routers in the path> time=0.001 ms

--- live.com ping statistics ---
1 packets transmitted, 1 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 0.001/0.001/0.001/0.000 ms

[asomers]

LGTM, including the TTL part.