scripts/posix_net_conf.sh: implement the logic for selecting default MQ mode
scripts/posix_net_conf.sh: implement the logic for selecting default MQ mode

If neither -mq nor -sq is given script will use a default mode:
    - If number of NIC's IRQs is greater than half of CPUs cores (not
      including hyperthreads) - use an '-mq' mode.
    - Otherwise if number or NIC's IRQs is greater than 7 - use an '-mq' mode.
    - Otherwise use an '-sq' mode.

See scylladb/scylla#1126.

Signed-off-by: Vlad Zolotarov <976c0f8d0852ed6439ad273880b400a75a7c41d0@cloudius-systems.com>
Message-Id: <1459449621-26048-3-git-send-email-976c0f8d0852ed6439ad273880b400a75a7c41d0@cloudius-systems.com>

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