libapi: Add missing linux/types.h header to get the __u64 type on io.h

There are functions using __u64, so we need to have the linux/types.h
header otherwise we'll break when its not included before api/io.h.

Fixes: e95770af4c ("tools api: Add a lightweight buffered reading api")
Reviewed-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/lkml/ZWjDPL+IzPPsuC3X@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/api/io.h

@@ -12,6 +12,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+#include <linux/types.h>
 
 struct io {
 	/* File descriptor being read/ */