struct defs changes for supporting shallow clone

* New struct `git_fetch_negotiation`
* New field `depth` for `git_fetch_options`
* New callback `git_transport->shallow_roots`.
* Updated `git_transport->negotiate_fetch` param with `git_fetch_negotiation`.
*

libgit2-sys/lib.rs

@@ -394,10 +394,20 @@ pub struct git_fetch_options {
     pub update_fetchhead: c_int,
     pub download_tags: git_remote_autotag_option_t,
     pub proxy_opts: git_proxy_options,
+    pub depth: c_int,
     pub follow_redirects: git_remote_redirect_t,
     pub custom_headers: git_strarray,
 }
 
+#[repr(C)]
+pub struct git_fetch_negotiation {
+    refs: *const *const git_remote_head,
+    refs_len: size_t,
+    shallow_roots: *mut git_oid,
+    shallow_roots_len: size_t,
+    depth: c_int,
+}
+
 git_enum! {
     pub enum git_remote_autotag_option_t {
         GIT_REMOTE_DOWNLOAD_TAGS_UNSPECIFIED,
@@ -1406,10 +1416,11 @@ pub struct git_transport {
         extern "C" fn(
             transport: *mut git_transport,
             repo: *mut git_repository,
-            refs: *const *const git_remote_head,
-            count: size_t,
+            fetch_data: *const git_fetch_negotiation,
         ) -> c_int,
     >,
+    pub shallow_roots:
+        Option<extern "C" fn(out: *mut git_oidarray, transport: *mut git_transport) -> c_int>,
     pub download_pack: Option<
         extern "C" fn(
             transport: *mut git_transport,

src/remote.rs

@@ -588,6 +588,7 @@ impl<'cb> Binding for FetchOptions<'cb> {
             prune: crate::call::convert(&self.prune),
             update_fetchhead: crate::call::convert(&self.update_fetchhead),
             download_tags: crate::call::convert(&self.download_tags),
+            depth: 0, // GIT_FETCH_DEPTH_FULL.
             follow_redirects: self.follow_redirects.raw(),
             custom_headers: git_strarray {
                 count: self.custom_headers_ptrs.len(),