seastar: pickup the recent future optimizations.

Signed-off-by: Radoslaw Zarzynski <rzarzyns@redhat.com>

diff --git a/src/seastar b/src/seastar
index 89a85fdd7b357d8cf55a392f312401a12a135a94..fb4d559f1417edd44580a44ee90c25c3cb76ea6e 160000 (submodule)
--- a/src/seastar
+++ b/src/seastar
@@ -1 +1 @@
-Subproject commit 89a85fdd7b357d8cf55a392f312401a12a135a94
+Subproject commit fb4d559f1417edd44580a44ee90c25c3cb76ea6e