Update seastar submodule
Update seastar submodule

* seastar affc3a5107...5eaec672a2 (12):
  > test_thread_custom_stack_size_failure: Use a larger custom stack
  > test_thread_custom_stack_size: Use a larger custom stack
  > log: correct help message
  > perftune.py: verify NIC existence
  > Merge "Fix various memory issues in http" from Rafael
  > build: Fix IN_LIST usage
  > future: Disable -Wuninitialized on a particular memcpy
  > build: use IN_LIST for shorter cmake
  > build: check support of "-fstack-clash-protection" before using it
  > configure.py: Add "--verbose" flag
  > configure.py: Make "cmake" command line human-readable
  > net: dynamically adjust buffer sizes for posix connected_socket read operations

avikivity/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla