opennds: [21.02] Backport of Release v9.1.1

opennds: [21.02] Backport of Release v9.1.1

Maintainer: Rob White rob@blue-wave.net
Compile tested: arm_cortex-a7_neon-vfpv4, mipsel_24kc
Run tested: arm_cortex-a7_neon-vfpv4, mipsel_24kc, gl-inet b1300, gl-inet mt300n-v2, Snapshot, 21.02.0-rc3, 19.07.7

Description:
This version fixes a compiler error, some compiler warnings and mutes a debug message
  * Fix - Compiler error, missing mode in call to open() [bluewave.net]
  * Fix - Compiler warning, ignored return value from call to lockf() [bluewave.net]
  * Fix - Compiler warning, ignored return value from call to system() [bluewave.net]
  * Fix - Compiler warning, ignored return value from call to fgets() [bluewave.net]
  * Fix - Remove debug message from call to get_client_interface library [bluewave.net]

Signed-off-by: Rob White <rob@blue-wave.net>