eal: add option to limit memory allocation on sockets

eal: add option to limit memory allocation on sockets

Previously, it was possible to limit maximum amount of memory
allowed for allocation by creating validator callbacks. Although a
powerful tool, it's a bit of a hassle and requires modifying the
application for it to work with DPDK example applications.

Fix this by adding a new parameter "--socket-limit", with syntax
similar to "--socket-mem", which would set per-socket memory
allocation limits, and set up a default validator callback to deny
all allocations above the limit.

This option is incompatible with legacy mode, as validator callbacks
are not supported there.

Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>