curl_gssapi: add a missing include of sendf.h

... to avoid build failure when GSS_C_DELEG_POLICY_FLAG is not defined.

Reported by: Paul Howarth

lib/curl_gssapi.c

@@ -25,9 +25,10 @@
 #ifdef HAVE_GSSAPI
 
 #include "curl_gssapi.h"
+#include "sendf.h"
 
 OM_uint32 Curl_gss_init_sec_context(
-    const struct SessionHandle *data,
+    struct SessionHandle *data,
     OM_uint32 * minor_status,
     gss_ctx_id_t * context,
     gss_name_t target_name,

lib/curl_gssapi.h

@@ -43,7 +43,7 @@
 /* Common method for using gss api */
 
 OM_uint32 Curl_gss_init_sec_context(
-    const struct SessionHandle *data,
+    struct SessionHandle *data,
     OM_uint32 * minor_status,
     gss_ctx_id_t * context,
     gss_name_t target_name,