Merge pull request #450 from sunghan-chang/menuconfig

refactor menuconfig structure

diff --cc os/Kconfig
Simple merge

diff --cc os/drivers/Kconfig
index aada052,a70518b..54b7b0b
--- 1/os/drivers/Kconfig
--- 2/os/drivers/Kconfig
+++ b/os/drivers/Kconfig
@@@ -17,11 -14,8 +17,9 @@@ config DEV_NUL
  config DEV_ZERO
        bool "Enable /dev/zero"
        default n
 +      depends on NFILE_DESCRIPTORS != 0
  
- menu "Buffering"
- 
- config DRVR_WRITEBUFFER
+ menuconfig DRVR_WRITEBUFFER
        bool "Enable write buffer support"
        depends on SCHED_WORKQUEUE
        default n