Fix several ARM nvram utility bugs

Fix several ARM nvram utility bugs

These fixes come directly from AsusWRT/Merlin.

nvram save -- would output every NVRAM key/value to stdout
due to #ifdef/#endif conditions being commented out

nvram restore -- depending on what characters were used in
NVRAM variables (keys or values), and the obfuscation method
involving random numbers implemented by Asus, it was possible
that certain values, ranges, or byte sequences of characters
may cause restoration problems.

nvram usage syntax -- restore showing the usage syntax if
there are no matching arguments, i.e. "nvram djdsjqd" should
now show usage syntax rather than nothing.

Reference: https://github.com/RMerl/asuswrt-merlin/blob/master/release/src/router/nvram_arm/main.c
Reference: http://www.linksysinfo.org/index.php?threads/tomato-arm-cfg-file.73093/#post-282981