Shall we change peer.ipv4 to String tag in golang impl?

[NeoCN]

I noticed that peer.ipv4 tag defined in ext package is uint32 type

// PeerHostIPv4 records IP v4 host address of the peer
PeerHostIPv4 = uint32TagName("peer.ipv4")

but , according to Standard Span tags and log fields, the peer.ipv4 tag is described as

--	--	--
peer.ipv4	string	Remote IPv4 address as a .-separated tuple. E.g., "127.0.0.1"
--	--	--

So, follow the conventions or keep the current code?

[yurishkuro]

we should not change the existing tag, it will be a breaking change that requires a new major version. We can add something like PeerHostIPv4Str with the same peer.ipv4 key but as a string tag, and add comments to PeerHostIPv4 to explain the reasoning.

@NeoCN are you ok to do a pull request?

[NeoCN]

@yurishkuro done!