extmod/modnetwork: Implement IPv6 API to set and get NIC configuration.

This commit implements a new <AbstractNIC>.ipconfig() function for the NIC
classes that use lwIP, to set and retrieve network configuration for a NIC.
Currently this method supports:
- ipconfig("addr4"): obtain a tuple (addr, netmask) of the currently
  configured ipv4 address
- ipconfig("addr6"): obtain a list of tuples (addr, state,
  prefered_lifetime, valid_lifetime) of all currently active ipv6
  addresses; this includes static, slaac and link-local addresses
- ipconfig("has_dhcp4"): whether ipv4 dhcp has supplied an address
- ipconfig("has_autoconf6"): if there is a valid, non-static ipv6 address
- ipconfig(addr4="1.2.3.4/24"): to set the ipv4 address and netmask
- ipconfig(addr6="2a01::2"): to set a static ipv6 address; note that this
  does not configure an interface route, as this does not seem supported by
  lwIP
- ipconfig(autoconf6=True): to enable ipv6 network configuration with slaac
- ipconfig(gw4="1.2.3.1"): to set the ipv4 gateway
- ipconfig(dhcp4=True): enable ipv4 dhcp; this sets ipv4 address, netmask,
  gateway and a dns server
- ipconfig(dhcp4=False): stops dhcp, releases the ip, and clears the
  configured ipv4 address.
- ipconfig(dhcp6=True): enable stateless dhcpv6 to obtain a dns server

There is also a new global configuration function network.ipconfig() that
supports the following:
- network.ipconfig(dns="2a01::2"): set the primary dns server (can be a
  ipv4 or ipv6 address)
- network.ipconfig(prefer=6): to prefer ipv6 addresses to be returned as
  dns responses (falling back to ipv4 if the host does not have an ipv6
  address); note that this does not flush the dns cache, so if a host is
  already in the dns cache with its v4 address, subsequent lookups will
  return that address even if prefer=6 is set

This interface replaces NIC.ifconfig() completely, and ifconfig() should be
marked as deprecated and removed in a future version.

Signed-off-by: Felix Dörre <felix@dogcraft.de>

extmod/modnetwork.c

@@ -141,10 +141,17 @@ mp_obj_t mod_network_hostname(size_t n_args, const mp_obj_t *args) {
 }
 static MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_network_hostname_obj, 0, 1, mod_network_hostname);
 
+#if LWIP_VERSION_MAJOR >= 2
+MP_DEFINE_CONST_FUN_OBJ_KW(mod_network_ipconfig_obj, 0, mod_network_ipconfig);
+#endif
+
 static const mp_rom_map_elem_t mp_module_network_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_network) },
     { MP_ROM_QSTR(MP_QSTR_country), MP_ROM_PTR(&mod_network_country_obj) },
     { MP_ROM_QSTR(MP_QSTR_hostname), MP_ROM_PTR(&mod_network_hostname_obj) },
+    #if LWIP_VERSION_MAJOR >= 2
+    { MP_ROM_QSTR(MP_QSTR_ipconfig), MP_ROM_PTR(&mod_network_ipconfig_obj) },
+    #endif
 
     // Defined per port in mpconfigport.h
     #ifdef MICROPY_PORT_NETWORK_INTERFACES