[Backport 5.4] mv gossip: check errno instead of value returned by strtoull

[mergify]

Currently, when a view update backlog is changed and sent
using gossip, we check whether the strtoll/strtoull
function used for reading the backlog returned
LLONG_MAX/ULLONG_MAX, signaling an error of a value
exceeding the type's limit, and if so, we do not store
it as the new value for the node.

However, the ULLONG_MAX value can also be used as the max
backlog size when sending empty backlogs that were never
updated. In theory, we could avoid sending the default
backlog because each node has its real backlog (based on
the node's memory, different than the ULLONG_MAX used in
the default backlog). In practice, if the node's
backlog changed to 0, the backlog sent by it will be
likely the default backlog, because when selecting
the biggest backlog across node's shards, we use the
operator<=>(), which treats the default backlog as
equal to an empty backlog and we may get the default
backlog during comparison if the backlog of some shard
was never changed (also it's the initial max value
we compare shard's backlogs against).

This patch removes the (U)LLONG_MAX check and replaces
it with the errno check, which is also set to ERANGE during
the strtoll error, and which won't prevent empty backlogs
from being read

Fixes: #18462

This patch should be backported to both 5.2 and 5.4 as it increases correctness and there should be no conflicts

(cherry picked from commit 64d133f)

Refs #18560

[scylladb-promoter]

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