Make skip_pages function available criu-wide

For the upcoming userfaultfd integration the skip_pages functionality is
required to find the userfaultfd requested pages.
Signed-off-by: Adrian Reber <areber@redhat.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/include/pagemap.h

@@ -49,6 +49,7 @@ struct page_read {
 	/* Advance page_read to the next entry (including zero pagemaps) */
 	int (*advance)(struct page_read *pr);
 	void (*close)(struct page_read *);
+	void (*skip_pages)(struct page_read *, unsigned long len);
 	int (*sync)(struct page_read *pr);
 	int (*seek_pagemap)(struct page_read *pr, unsigned long vaddr);
 

criu/pagemap.c

@@ -698,6 +698,7 @@ int open_page_read_at(int dfd, int pid, struct page_read *pr, int pr_flags)
 	pr->read_pages = read_pagemap_page;
 	pr->advance = advance;
 	pr->close = close_page_read;
+	pr->skip_pages = skip_pagemap_pages;
 	pr->sync = process_async_reads;
 	pr->seek_pagemap = seek_pagemap;
 	pr->id = ids++;