Branch b_release_1_8_1

Branch b_release_1_8_1
b=18092

fix following warning:
cc1: warnings being treated as errors
/cache/build/BUILD/lustre-1.8.0.123/lnet/libcfs/linux/linux-debug.c:215:
warning: 'print_trace_warning_symbol' defined but not used
/cache/build/BUILD/lustre-1.8.0.123/lnet/libcfs/linux/linux-debug.c:222:
warning: 'print_trace_warning' defined but not used
/cache/build/BUILD/lustre-1.8.0.123/lnet/libcfs/linux/linux-debug.c:227:
warning: 'print_trace_stack' defined but not used
/cache/build/BUILD/lustre-1.8.0.123/lnet/libcfs/linux/linux-debug.c:242:
warning: 'print_trace_address' defined but not used