PMM-7689 Updated data type for getLastErrorDefaults.w (#484)

This field is not being used by any tool but it is needed to decode
bigger structures having it. Since the value can be an int to indicate
the number 1-primary, etc, or 'majority', I've changed the field type
from int to interface{}

src/go/mongolib/proto/replstatus.go

@@ -75,8 +75,8 @@ type RSConfig struct {
 }
 
 type LastErrorDefaults struct {
-	W        int32 `bson:"w"`
-	WTimeout int32 `bson:"wtimeout"`
+	W        interface{} `bson:"w"`
+	WTimeout int32       `bson:"wtimeout"`
 }
 
 type RSSettings struct {