sys/mman.h: add MADV_COLLAPSE from linux v6.1

Add madvise flag which performs a best-effort synchronous
collapse of the native pages mapped by the memory range
into Transparent Huge Pages (THPs)
see
  linux commit 7d8faaf155454f8798ec56404faca29a82689c77
  mm/madvise: introduce MADV_COLLAPSE sync hugepage collapse

include/sys/mman.h

@@ -98,6 +98,7 @@ extern "C" {
 #define MADV_POPULATE_READ 22
 #define MADV_POPULATE_WRITE 23
 #define MADV_DONTNEED_LOCKED 24
+#define MADV_COLLAPSE    25
 #define MADV_HWPOISON    100
 #define MADV_SOFT_OFFLINE 101
 #endif