elf: Add kprobe EventNameOption for unique eventName per Module

[intr3p1d]

#251 : can't attach two functions for the same kprobe event
#271 : make uprobe eventname with symbol address (maybe similar issue)

Intention

Currently, gobpf/elf Module make kprobe eventName like this:

gobpf/elf/module.go

Line 359 in 2289761

eventName := probeType + funcName

gobpf/elf/module.go

Lines 746 to 751 in 2289761

	if isKretprobe {
	funcName = strings.TrimPrefix(name, "kretprobe/")
	err = disableKprobe("r" + funcName)
	} else {
	funcName = strings.TrimPrefix(name, "kprobe/")
	err = disableKprobe("p" + funcName)

Such a naming works well when we use it temporarily.
However, this situation can happen: (Also I get stuck)

1. Program 1 attaches a probe at an address (such as kprobe/tcp_sendmsg)
2. Program 2 attaches a probe at the address
3. Even though eBPF allows multiple probes at the same address*, error occurred: "could not enable kprobe_events: file exists"

*The Kernel document says that we can actually attach two different probes at the same address.
https://www.kernel.org/doc/Documentation/kprobes.txt : 5. Kprobes Features and Limitations

I know that this issue is a little tricky to handle in the library. I tried to fix this issue in my use.
But It was much more tricky to handle unexported fields and methods... So I made this PR.

Changed Files

• elf/module.go : Add a field kprobeEvOpts EventNameOption in Module therefore we can seperate a namespace of each Module.
• elf/module_unsupported.go : Adjust for unsupported module

Need to Fix

• Change gobpf/bcc.Module to work same as above.
• Move the body of TrySetKprobeEventNameOpts() to the constructor of elf.Module (?)
  - There are already 4 constructor in elf.Module such as... : NewModuleWithLog, NewModuleFromReaderWithLog, NewModule, NewModuleFromReader. Therefore I didn't make additional constructor.