Add return value check and error handling for fseek call.
Coverity issue: 143435
Fixes: 361b2e9559fc ("acl: new sample l3fwd-acl")
Signed-off-by: Kuba Kozak <kubax.kozak@intel.com> Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com> Acked-by: Zhiyong Yang <zhiyong.yang@intel.com>