bpftool: Update documentation of "bpftool feature" command

FEATURE COMMANDS

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|	**bpftool** **feature probe** [*COMPONENT*] [**macros** [**prefix** *PREFIX*]]

|	**bpftool** **feature probe** [*COMPONENT*] [**full**] [**macros** [**prefix** *PREFIX*]]

|	**bpftool** **feature help**

|

|	*COMPONENT* := { **kernel** | **dev** *NAME* }

DESCRIPTION

===========

	**bpftool feature probe** [**kernel**] [**macros** [**prefix** *PREFIX*]]

	**bpftool feature probe** [**kernel**] [**full**] [**macros** [**prefix** *PREFIX*]]

		  Probe the running kernel and dump a number of eBPF-related

		  parameters, such as availability of the **bpf()** system call,

		  JIT status, eBPF program types availability, eBPF helper

		  functions availability, and more.

		  By default, bpftool **does not run probes** for

		  **bpf_probe_write_user**\ () and **bpf_trace_printk**\()

		  helpers which print warnings to kernel logs. To enable them

		  and run all probes, the **full** keyword should be used.

		  If the **macros** keyword (but not the **-j** option) is

		  passed, a subset of the output is dumped as a list of

		  **#define** macros that are ready to be included in a C

		  Keyword **kernel** can be omitted. If no probe target is

		  specified, probing the kernel is the default behaviour.

		  Note that when probed, some eBPF helpers (e.g.

		  **bpf_trace_printk**\ () or **bpf_probe_write_user**\ ()) may

		  print warnings to kernel logs.

	**bpftool feature probe dev** *NAME* [**macros** [**prefix** *PREFIX*]]

	**bpftool feature probe dev** *NAME* [**full**] [**macros** [**prefix** *PREFIX*]]

		  Probe network device for supported eBPF features and dump

		  results to the console.

		  The two keywords **macros** and **prefix** have the same

		  role as when probing the kernel.

		  The keywords **full**, **macros** and **prefix** have the

		  same role as when probing the kernel.

	**bpftool feature help**

		  Print short help message.