"This series fixes the user after free issue in gossip and elimates the
duplicated / unnecessary mark alive operations.
Fixes#2341"
* tag 'asias/gossip_fix_mark_alive/v1' of github.com:cloudius-systems/seastar-dev:
gossip: Ignore callbacks and mark alive operation in shadow round
gossip: Ingore the duplicated mark alive operation
gossip: Fix user after free in mark_alive
(cherry picked from commit 1e04731fa0)