Define default parameters of functions of derived class the same as the base class

The member function bringup() of class ThreadInterface redefines
parameter stack's default value to IPV6_STACK from the inherited default value
DEFAULT_STACK (in Interface).
The default value will be resolved statically, not by dispatch, so this
can cause confusion.
Similar arguments apply to LoWPANNDInterface and WisunInterface.

Author: szsam

connectivity/nanostack/mbed-mesh-api/source/LoWPANNDInterface.cpp

@@ -28,7 +28,7 @@ class Nanostack::LoWPANNDInterface final : public Nanostack::MeshInterface {
 public:
     nsapi_error_t bringup(bool dhcp, const char *ip,
                           const char *netmask, const char *gw,
-                          nsapi_ip_stack_t stack = IPV6_STACK,
+                          nsapi_ip_stack_t stack = DEFAULT_STACK,
                           bool blocking = true) override;
     nsapi_error_t bringdown() override;
     nsapi_error_t get_gateway(SocketAddress *sockAddr) override;

connectivity/nanostack/mbed-mesh-api/source/ThreadInterface.cpp

@@ -27,7 +27,7 @@ class Nanostack::ThreadInterface : public Nanostack::MeshInterface {
 public:
     nsapi_error_t bringup(bool dhcp, const char *ip,
                           const char *netmask, const char *gw,
-                          nsapi_ip_stack_t stack = IPV6_STACK,
+                          nsapi_ip_stack_t stack = DEFAULT_STACK,
                           bool blocking = true) override;
     nsapi_error_t bringdown() override;
     friend class Nanostack;

connectivity/nanostack/mbed-mesh-api/source/WisunInterface.cpp

@@ -34,7 +34,7 @@ class Nanostack::WisunInterface final : public Nanostack::MeshInterface {
 public:
     nsapi_error_t bringup(bool dhcp, const char *ip,
                           const char *netmask, const char *gw,
-                          nsapi_ip_stack_t stack = IPV6_STACK,
+                          nsapi_ip_stack_t stack = DEFAULT_STACK,
                           bool blocking = true) override;
     nsapi_error_t bringdown() override;
     nsapi_error_t get_gateway(SocketAddress *address) override;