seastar: pickup change to add pthread linkage

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

diff --git a/src/seastar b/src/seastar
index 119ce3303542c572e425384e451432ed1abf9bc9..2670723feec5fc99d1f709aaf6fd3dc2b17a3f70 160000 (submodule)
--- a/src/seastar
+++ b/src/seastar
@@ -1 +1 @@
-Subproject commit 119ce3303542c572e425384e451432ed1abf9bc9
+Subproject commit 2670723feec5fc99d1f709aaf6fd3dc2b17a3f70