dpdk: Limit DPDK memory usage.

dpdk: Limit DPDK memory usage.

Since 18.05 release, DPDK moved to dynamic memory model in which
hugepages could be allocated on demand. At the same time '--socket-mem'
option was re-defined as a size of pre-allocated memory, i.e. memory
that should be allocated at startup and could not be freed.
So, DPDK with a new memory model could allocate more hugepage memory
than specified in '--socket-mem' or '-m' options.

This change adds new configurable 'other_config:dpdk-socket-limit'
which could be used to limit the ammount of memory DPDK could use.
It uses new DPDK option '--socket-limit'.
Ex.:

  ovs-vsctl set Open_vSwitch . other_config:dpdk-socket-limit="1024,1024"

Also, in order to preserve old behaviour, if '--socket-limit' is not
specified, it will be defaulted to the amount of memory specified by
'--socket-mem' option, i.e. OVS will not be able to allocate more.
This is needed, for example, to disallow OVS to allocate more memory
than reserved for it by Nova in OpenStack installations.

Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>