NetworkPkg/MnpDxe: Fix various typos

NetworkPkg/MnpDxe: Fix various typos

Fix various typos in documentation, comments and debug strings.

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: <20200207010831.9046-44-philmd@redhat.com>
[lersek@redhat.com: replace EFI_D_xxx w/ DEBUG_xxx to shut up PatchCheck]