[RFE] buffer copy limited handlings, especially in IPC code (possibly with OS-specific tweaks)

Thought this is already filed but apparently it's not and it came up the
memories when I stumbled upon https://gerrit.asterisk.org/#/c/asterisk/+/5857/

Note that there are some zero-copy measures in corosync itself
(see `zcb_` symbols). Also, presumably `dbus-broker` will contain some
good examples of how to avoid extraneous copies even if it might be
just Linux specific).