Fix heap-buffer-overflow in osquery::tables::netmaskFromIP
Fix heap-buffer-overflow in osquery::tables::netmaskFromIP

Issue highlighted by asan activated in PR osquery/osquery#5628

Do not try to read the destination address of a netmask if such address
is a default route.

PR: osquery/osquery#5665

hackgnar/osquery,hackgnar/osquery,hackgnar/osquery