buildtools: remove make-specific from symbols check
buildtools: remove make-specific from symbols check

The check-experimental-syms.sh script was finding the map-list-symbol.sh
script using $RTE_SDK, which is the variable set when using the "make"
build system. To make this script more independent, we just use the current
path of the script as the location to find its companion script.

Signed-off-by: Bruce Richardson <66b9e8e8fbd5e9f41f91b0af050876182ce9d0e4@intel.com>
Acked-by: Luca Boccassi <020748dc039465edc3ee6f30c530b21164cdce27@debian.org>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk