internode lockArgs should use messagepack (#13329)

it would seem like using `bufio.Scan()` is very
slow for heavy concurrent I/O, ie. when r.Body
is slow , instead use a proper
binary exchange format, to marshal and unmarshal
the LockArgs datastructure in a cleaner way.

this PR increases performance of the locking
sub-system for tiny repeated read lock requests
on same object.

```
BenchmarkLockArgs
BenchmarkLockArgs-4              6417609               185.7 ns/op            56 B/op          2 allocs/op
BenchmarkLockArgsOld
BenchmarkLockArgsOld-4           1187368              1015 ns/op            4096 B/op          1 allocs/op
```

internal/dsync/rpc-client-interface.go

@@ -19,26 +19,6 @@ package dsync
 
 import "context"
 
-// LockArgs is minimal required values for any dsync compatible lock operation.
-type LockArgs struct {
-	// Unique ID of lock/unlock request.
-	UID string
-
-	// Resources contains single or multiple entries to be locked/unlocked.
-	Resources []string
-
-	// Source contains the line number, function and file name of the code
-	// on the client node that requested the lock.
-	Source string
-
-	// Owner represents unique ID for this instance, an owner who originally requested
-	// the locked resource, useful primarily in figuring our stale locks.
-	Owner string
-
-	// Quorum represents the expected quorum for this lock type.
-	Quorum int
-}
-
 // NetLocker is dsync compatible locker interface.
 type NetLocker interface {
 	// Do read lock for given LockArgs.  It should return