MINOR: global: define MODE_STOPPING

Define a new mode MODE_STOPPING. It is used to indicate that the process
is in the stopping stage and no event loop runs anymore.

(cherry picked from commit 7afa5c1843521ec3be7549592d2b38ccc9d68b73)
[ad: adjusted context: check mode not implemented in 2.4]
Signed-off-by: Amaury Denoyelle <adenoyelle@haproxy.com>
2 files changed