doc: fix ethtool app path
doc: fix ethtool app path

The path to the ethtool application was slightly incorrect in the
documentation. This patch corrects that path.

Fixes: bda68ab9d1e7 ("examples/ethtool: add user-space ethtool sample application")
Cc: stable@dpdk.org

Signed-off-by: Sarosh Arif <701b58c7cb2b006b3a7612646904b47eba236db5@emumba.com>

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