all: Support multiple device connections (fixes #141) (#8918)

This adds the ability to have multiple concurrent connections to a single device. This is primarily useful when the network has multiple physical links for aggregated bandwidth. A single connection will never see a higher rate than a single link can give, but multiple connections are load-balanced over multiple links.

It is also incidentally useful for older multi-core CPUs, where bandwidth could be limited by the TLS performance of a single CPU core -- using multiple connections achieves concurrency in the required crypto calculations...

Co-authored-by: Simon Frei <freisim93@gmail.com>
Co-authored-by: tomasz1986 <twilczynski@naver.com>
Co-authored-by: bt90 <btom1990@googlemail.com>

lib/protocol/nativemodel_windows.go

@@ -13,20 +13,20 @@ import (
 	"strings"
 )
 
-func makeNative(m contextLessModel) contextLessModel { return nativeModel{m} }
+func makeNative(m rawModel) rawModel { return nativeModel{m} }
 
 type nativeModel struct {
-	contextLessModel
+	rawModel
 }
 
 func (m nativeModel) Index(folder string, files []FileInfo) error {
 	files = fixupFiles(files)
-	return m.contextLessModel.Index(folder, files)
+	return m.rawModel.Index(folder, files)
 }
 
 func (m nativeModel) IndexUpdate(folder string, files []FileInfo) error {
 	files = fixupFiles(files)
-	return m.contextLessModel.IndexUpdate(folder, files)
+	return m.rawModel.IndexUpdate(folder, files)
 }
 
 func (m nativeModel) Request(folder, name string, blockNo, size int32, offset int64, hash []byte, weakHash uint32, fromTemporary bool) (RequestResponse, error) {
@@ -36,7 +36,7 @@ func (m nativeModel) Request(folder, name string, blockNo, size int32, offset in
 	}
 
 	name = filepath.FromSlash(name)
-	return m.contextLessModel.Request(folder, name, blockNo, size, offset, hash, weakHash, fromTemporary)
+	return m.rawModel.Request(folder, name, blockNo, size, offset, hash, weakHash, fromTemporary)
 }
 
 func fixupFiles(files []FileInfo) []FileInfo {