streams: handle short writes only in generic stream

Now that the function `git_stream__write_full` exists and callers of
`git_stream_write` have been adjusted, we can lift logic for short
writes out of the stream implementations. Instead, this is now handled
either by `git_stream__write_full` or by callers of `git_stream_write`
directly.

src/streams/mbedtls.c

@@ -303,20 +303,15 @@ static int mbedtls_set_proxy(git_stream *stream, const git_proxy_options *proxy_
 	return git_stream_set_proxy(st->io, proxy_options);
 }
 
-static ssize_t mbedtls_stream_write(git_stream *stream, const char *data, size_t data_len, int flags)
+static ssize_t mbedtls_stream_write(git_stream *stream, const char *data, size_t len, int flags)
 {
-	ssize_t written = 0, len = min(data_len, SSIZE_MAX);
 	mbedtls_stream *st = (mbedtls_stream *) stream;
+	int written;
 
 	GIT_UNUSED(flags);
 
-	do {
-		int error = mbedtls_ssl_write(st->ssl, (const unsigned char *)data + written, len - written);
-		if (error <= 0) {
-			return ssl_set_error(st->ssl, error);
-		}
-		written += error;
-	} while (written < len);
+	if ((written = mbedtls_ssl_write(st->ssl, (const unsigned char *)data, len)) <= 0)
+		return ssl_set_error(st->ssl, written);
 
 	return written;
 }

src/streams/socket.c

@@ -130,23 +130,19 @@ static int socket_connect(git_stream *stream)
 	return 0;
 }
 
-static ssize_t socket_write(git_stream *stream, const char *data, size_t data_len, int flags)
+static ssize_t socket_write(git_stream *stream, const char *data, size_t len, int flags)
 {
-	ssize_t ret, off = 0, len = min(data_len, SSIZE_MAX);
 	git_socket_stream *st = (git_socket_stream *) stream;
+	ssize_t written;
 
-	while (off < len) {
 	errno = 0;
-		ret = p_send(st->s, data + off, len - off, flags);
-		if (ret < 0) {
+
+	if ((written = p_send(st->s, data, len, flags)) < 0) {
 		net_set_error("Error sending data");
 		return -1;
 	}
 
-		off += ret;
-	}
-
-	return off;
+	return written;
 }
 
 static ssize_t socket_read(git_stream *stream, void *data, size_t len)