more _KERNEL_OPT
prettify and add to all the modules that have it.
Ensure callout isn't running and pending before callout_destroy

Call callout_halt before callout_destroy. And also let callout (mld_timeo)
not call callout_schedule when we already called callout_halt.

This fixes PR 47881.
PR/47704: Takahiro HAYASHI: Add -L flag
PR/47704: Takahiro HAYASHI: Fix -L flag
Add compatmodules keyword so that build.sh -V MKCOMPATMODULES=no won't fail.
List missing compatmodules keyword in the comment.
fix description setting.
Allow setxattr to be called with a NULL value, instead of crashing.