Use in_addr in ip_mreq_source and ip_msfilter.

This adds a new mechanism to say "replace struct S with #include <bits/S.h>".

Also switch epoll_event over to the new mechanism.

Also use the kernel's struct sockaddr_storage directly rather than behind
an unnecessary #define.

This patch also removes some dead code in the header scrubber. This code
still needs rewriting completely. I learned that a "block" isn't necessarily
a single struct definition, say; it might be a run of them. It seems like
a block is a run of preprocessor directives or a run of regular code.

Bug: https://issuetracker.google.com/36987220
Test: new test
Change-Id: Ic6a5c09559766a4babe3cd4c3ea538b885e07308
diff --git a/libc/kernel/uapi/linux/eventpoll.h b/libc/kernel/uapi/linux/eventpoll.h
index d0a5f6e..eec1077 100644
--- a/libc/kernel/uapi/linux/eventpoll.h
+++ b/libc/kernel/uapi/linux/eventpoll.h
@@ -18,6 +18,7 @@
  ****************************************************************************/
 #ifndef _UAPI_LINUX_EVENTPOLL_H
 #define _UAPI_LINUX_EVENTPOLL_H
+#include <bits/epoll_event.h>
 #include <linux/fcntl.h>
 #include <linux/types.h>
 #define EPOLL_CLOEXEC O_CLOEXEC
@@ -44,8 +45,4 @@
 #else
 #define EPOLL_PACKED
 #endif
-struct __kernel_uapi_epoll_event {
-  __u32 events;
-  __u64 data;
-} EPOLL_PACKED;
 #endif