oshmem: fixup hostname max length usage

Signed-off-by: Karol Mroz <mroz.karol@gmail.com>

oshmem/runtime/oshmem_shmem_abort.c

@@ -42,7 +42,7 @@ static bool have_been_invoked = false;
 
 int oshmem_shmem_abort(int errcode)
 {
-    char *host, hostname[MAXHOSTNAMELEN];
+    char *host, hostname[OPAL_MAXHOSTNAMELEN];
     pid_t pid = 0;
 
     /* Protection for recursive invocation */