sbin/ping: allow normal users to specify larger packets

[pfg]

Summary

Only super-user could specify a packet size larger than the default 56 bytes.
This restriction was added by Matt Dillon in 1998 during the BEST days [0].
This restriction doesn't exist in ping IPV6 or on NetBSD, OpenBSD and Linux.

UMS [1] uses this feature to estimate the client's bandwidth to optimize the
streaming experience.

[0] Git 526f06b278d9252add168aa18b60242c08771165
[1] UMS: https://github.com/UniversalMediaServer/UniversalMediaServer

Obtained from: DragonFlyBSD

Sidenotes: MAXICMPLEN seems to be unused in the current code and I had to sign cast a value in MAXIPLEN to make the compiler happy.

[zlei]

So the kernel does not have a real limit ( only super-user could specify a packet size larger than the default 56 bytes ) ?

[delphij]

sbin/ping/ping.c

461–464

I think this is actually redundant (code below would check and calculate a more accurate limit).

[pfg]

sbin/ping/ping.c

461–464

While the check does seem redundant and is only for non-root, the case only applies when "-s" is specified. Other checks may not apply

Hmm... would you mean just making -s a no-op?

[jlduran_gmail.com]

@kp has fixed the ping test in 2926c2594249f64fecbbdcb0b0b9a3591931ab04. It was not related to this commit.