common/options: add osd_map_message_max_bytes

common/options: add osd_map_message_max_bytes

Limit MOSDMap message size by bytes as well as map count.

Signed-off-by: Sage Weil <sage@redhat.com>
(cherry picked from commit e15be00560c1492e0807d0779cfd0d6088396b3e)

Conflicts:
	src/common/config_values.h: the changes in this file is applied
to src/common/config.h instead. because, src/common/config_values.h
is extracted in 4718b7cb2fac65b2ac7014f42ba1a10181350f0b. which
happened after luminous, and that commit was not backported.
  also, the OPT_SIZE is changed to OPT_U64, as we don't have OPT_SIZE by
then, the size_t option support was added after luminous, and that
change was not backported. so let's use the uint64_t as an alternative,
as other *bytes settings are also using OPT_U64. and OSDMonitor.cc
will be accessing that setting using the legacy way instead of using
conf.get_val<>() interface, so this change will have no impact on the
fix.