NetworkPkg/Ip6Dxe: Fix various typos

Fix various typos in comments and documentation.

Cc: Jiaxin Wu <jiaxin.wu@intel.com>
Cc: Siyuan Fu <siyuan.fu@intel.com>
Cc: Maciej Rabeda <maciej.rabeda@intel.com>
Signed-off-by: Antoine Coeur <coeur@gmx.fr>
Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>
Reviewed-by: Maciej Rabeda <maciej.rabeda@intel.com>
Signed-off-by: Philippe Mathieu-Daude <philmd@redhat.com>
Message-Id: <20200207010831.9046-41-philmd@redhat.com>

NetworkPkg/Ip6Dxe/Ip6Output.c

@@ -870,7 +870,7 @@ Ip6Output (
 
     for (Index = 0, Offset = 0, PacketLen = Mtu; Index < Num; Index++) {
       //
-      // Get fragment from the Packet, append UnFragnmentLen spare buffer
+      // Get fragment from the Packet, append UnFragmentLen spare buffer
       // before the fragmented data, the corresponding data is filled in later.
       //
       Fragment = NetbufGetFragment (Packet, Offset, PacketLen, UnFragmentLen);