eal: check string parameter lengths
When specifying parameters such as hugefile prefix from the
command-line, it is possibly to supply an empty string. This may
lead to various problems: for example, if hugefile prefix is
empty, the runtime config path construction may end up
looking like "/var/run/dpdk//_config", which will technically
work, but is wrong and places files in the wrong place.
To fix it, check lengths of such user-specified parameters for
hugefile prefix, as well as hugepage dir and user-specified
mbuf pool ops string.
Cc: stable@dpdk.org
Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>