seastar: pickup change to always enable smp poller

this is the first commit which is in sync with upstream without any
addition change in our branch.

Signed-off-by: Kefu Chai <kchai@redhat.com>

diff --git a/src/seastar b/src/seastar
index 2670723feec5fc99d1f709aaf6fd3dc2b17a3f70..663f9bb6cb2b20feb8448674eaa6a743cd513e5a 160000 (submodule)
--- a/src/seastar
+++ b/src/seastar
@@ -1 +1 @@
-Subproject commit 2670723feec5fc99d1f709aaf6fd3dc2b17a3f70
+Subproject commit 663f9bb6cb2b20feb8448674eaa6a743cd513e5a