msg/async/ProtocolV1: resurrect "include MGR as service when applying cephx settings"

msg/async/ProtocolV1: resurrect "include MGR as service when applying cephx settings"

This was added in commit 0ec7d6bbc4af ("msg/async,simple: include MGR
as service when applying cephx settings") and inadvertently dropped in
commit e6f043f7d2dc ("msgr/async: huge refactoring of protocol V1").
As a result, mgr daemons are miscategorized as clients when enforcing
cephx_*require_signatures options.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
(cherry picked from commit 949e2e595eda553aa68f697cee1dcfff3c09cf3f)