docs: clarify that --data-path-addr doesn't restrict access

[dvdksn]

- What I did

Added a paragraph that clarifies the scope of the --data-path-addr for docker swarm init.

Relates to moby/moby#47667

- How I did it

- How to verify it

- Description for the changelog

- A picture of a cute animal (not mandatory but encouraged)

[dvdksn]

cc @corhere

[codecov-commenter]

Codecov Report

Merging #4997 (faf096b) into master (c23a404) will decrease coverage by 0.03%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4997      +/-   ##
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- Coverage   61.04%   61.02%   -0.03%     
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  Files         295      295              
  Lines       20648    20648              
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- Hits        12605    12600       -5     
- Misses       7147     7150       +3     
- Partials      896      898       +2     

[thaJeztah]

Wondering if we should borrow some wording from --advertise-addr. Effectively (if my interpretation is correct here), --data-path-addr is advertising the address to use (I guess in hindsight, the flag should've been named to reflect that?)

cli/docs/reference/commandline/swarm_init.md

Lines 95 to 109 in c23a404

	### <a name="advertise-addr"></a> Specify interface for outbound control plane traffic (--advertise-addr)
	The `--advertise-addr` flag specifies the address that will be advertised to
	other members of the swarm for API access and overlay networking. If
	unspecified, Docker will check if the system has a single IP address, and use
	that IP address with the listening port (see `--listen-addr`). If the system
	has multiple IP addresses, `--advertise-addr` must be specified so that the
	correct address is chosen for inter-manager communication and overlay
	networking.
	It is also possible to specify a network interface to advertise that
	interface's address; for example `--advertise-addr eth0:2377`.
	Specifying a port is optional. If the value is a bare IP address or interface
	name, the default port 2377 is used.