Allow clock skew in krb5 gss_context_time()

Commit b496ce4 (ticket #8268) adds
the clock skew to krb5 acceptor context lifetimes for
gss_accept_sec_context() and gss_inquire_context(), but not for
gss_context_time().  Add the clock skew in gss_context_time() as well.

(cherry picked from commit b0a072e)

ticket: 8581
version_fixed: 1.15.2

src/lib/gssapi/krb5/context_time.c

@@ -51,7 +51,10 @@ krb5_gss_context_time(minor_status, context_handle, time_rec)
         return(GSS_S_FAILURE);
     }
 
-    if ((lifetime = ctx->krb_times.endtime - now) <= 0) {
+    lifetime = ctx->krb_times.endtime - now;
+    if (!ctx->initiate)
+        lifetime += ctx->k5_context->clockskew;
+    if (lifetime <= 0) {
         *time_rec = 0;
         *minor_status = 0;
         return(GSS_S_CONTEXT_EXPIRED);