96b_nitrogen.conf: Hard code BT settings

Nitrogen doesn't have other types of the network connectivity
beside BLE over IPv6 so apply required configuration within
board's config.

Signed-off-by: Zbigniew Bodek <zbigniew.bodek@huawei.com>

boards/96b_nitrogen.conf

 # Networking Config:
 CONFIG_NET_IPV4=n
 CONFIG_NET_IPV6=y
+CONFIG_NET_CONFIG_NEED_IPV6=y
+CONFIG_NET_CONFIG_NEED_IPV4=n
 
 # Disable unneeded settings from the base prj.conf:
 CONFIG_TEST_RANDOM_GENERATOR=n
@@ -11,3 +13,14 @@ CONFIG_NET_CONFIG_PEER_IPV4_ADDR=""
 # Specify networking addresses
 CONFIG_NET_CONFIG_MY_IPV6_ADDR=""
 CONFIG_NET_CONFIG_PEER_IPV6_ADDR=""
+
+# BLE Config:
+CONFIG_BT=y
+CONFIG_BT_DEBUG_LOG=y
+CONFIG_BT_SMP=y
+CONFIG_BT_PERIPHERAL=y
+CONFIG_BT_CENTRAL=y
+CONFIG_BT_L2CAP_DYNAMIC_CHANNEL=y
+CONFIG_BT_DEVICE_NAME="Zephyr MQTT"
+CONFIG_NET_L2_BT=y
+CONFIG_NET_CONFIG_BT_NODE=y