Update client.go: set peer.address tag from req.URL.Host; log hostPort in getConn()

[krantideep95]

while creating spans for outbound requests,
http.url tag is set In RoundTripper here:

go-stdlib/nethttp/client.go

Line 188 in 60eb967

ext.HTTPUrl.Set(tracer.sp, tracer.opts.urlTagFunc(req.URL))

but, if clientTrace is enabled, this http.url is overriden in getConn() with host:port. This leaves span with poorer data with just host:port instead of complete (sanitised, if URLTagFunc was passed) url.
Some tools like https://www.hypertrace.org/ depend on http.url tag to determine backends of a service, for which they require a complete url.

Edit: based on conversation in #3 (comment), made changes to set peer.address tag & log hostPort in getConn()

[yurishkuro]

lgtm, thanks