fastboot: Cap max size sent to libsparse

This is required for large (>INT_MAX) sparse limit reported by
the target.

Also, patch up return chains of "int" that need to deal with sizes
bigger than 2GB as well as return negative error codes.

Test: -S works with large max-download-size
Test: Flash 3GB system.img with max-download-size 2.5GB

Bug: 36810152
Change-Id: I562a50eabd706bd5b97c71a1aef07c1ffd1a2e5c
diff --git a/fastboot/fastboot.h b/fastboot/fastboot.h
index 6699b6a..b62a2d8 100644
--- a/fastboot/fastboot.h
+++ b/fastboot/fastboot.h
@@ -41,7 +41,7 @@
 /* protocol.c - fastboot protocol */
 int fb_command(Transport* transport, const char* cmd);
 int fb_command_response(Transport* transport, const char* cmd, char* response);
-int fb_download_data(Transport* transport, const void* data, uint32_t size);
+int64_t fb_download_data(Transport* transport, const void* data, uint32_t size);
 int fb_download_data_sparse(Transport* transport, struct sparse_file* s);
 const std::string fb_get_error();
 
@@ -64,7 +64,7 @@
 void fb_queue_download(const char *name, void *data, uint32_t size);
 void fb_queue_notice(const char *notice);
 void fb_queue_wait_for_disconnect(void);
-int fb_execute_queue(Transport* transport);
+int64_t fb_execute_queue(Transport* transport);
 void fb_set_active(const char *slot);
 
 /* util stuff */