Spi-hdlc-adapter: Mark unused fn return values, fix comments (#1128)
Spi-hdlc-adapter: Mark unused fn return values, fix comments (#1128)

This commit makes the following changes in spi-hdlc-adapter:

- It adds `IGNORE_RETURN_VALUE()` macro for cases where the returned
  value from a function can/should be safely ignored.

- It creates a local max 32 bytes string copy of the program name
  from `argv[0]` (to ensure the length is limited).

- It fixes some of the typos in comments.
vaas-krish/openthread,gandreello/openthread,GiedriusM/openthread,jjlee9/openthread,LeZhang2016/openthread,erja-gp/openthread,Zolertia/openthread,openthread/openthread,erja-gp/openthread,LeZhang2016/openthread,mszczodrak/openthread,gandreello/openthread,LeZhang2016/openthread,Zolertia/openthread,librasungirl/openthread,JakubBrachTieto/openthread,Zolertia/openthread,vaas-krish/openthread,Zolertia/openthread,gandreello/openthread,aeliot/openthread,lanyuwen/openthread,xiaom-GitHub/openthread,JakubBrachTieto/openthread,openthread/openthread,georgecpr/openthread,chshu/openthread,fbsder/openthread,LeZhang2016/openthread,turon/openthread,xiaom-GitHub/openthread,turon/openthread,xiaom-GitHub/openthread,gandreello/openthread,georgecpr/openthread,abtink/openthread,srickardti/openthread,nibanks/openthread,abtink/openthread,chshu/openthread,GiedriusM/openthread,LeZhang2016/openthread,pvanhorn/openthread,pvanhorn/openthread,jjlee9/openthread,GiedriusM/openthread,erja-gp/openthread,georgecpr/openthread,fbsder/openthread,openthread/openthread,pvanhorn/openthread,lanyuwen/openthread,GiedriusM/openthread,fbsder/openthread,librasungirl/openthread,jwhui/openthread,vaas-krish/openthread,JakubBrachTieto/openthread,aeliot/openthread,pvanhorn/openthread,jjlee9/openthread,jjlee9/openthread,srickardti/openthread,jwhui/openthread,jjlee3/openthread,JakubBrachTieto/openthread,aeliot/openthread,nibanks/openthread,librasungirl/openthread,lanyuwen/openthread,fbsder/openthread,georgecpr/openthread,jjlee3/openthread,jjlee9/openthread,chshu/openthread,erja-gp/openthread,vaas-krish/openthread,pvanhorn/openthread,jjlee3/openthread,bukepo/openthread,mszczodrak/openthread,jwhui/openthread,lanyuwen/openthread,mszczodrak/openthread,vaas-krish/openthread,chshu/openthread,georgecpr/openthread,jjlee3/openthread,xiaom-GitHub/openthread,aeliot/openthread,gandreello/openthread,librasungirl/openthread,LeZhang2016/openthread,xiaom-GitHub/openthread,turon/openthread,mszczodrak/openthread,bukepo/openthread,chshu/openthread,Zolertia/openthread,nibanks/openthread,georgecpr/openthread,chshu/openthread,mszczodrak/openthread,lanyuwen/openthread,erja-gp/openthread,aeliot/openthread,jjlee9/openthread,JakubBrachTieto/openthread,xiaom-GitHub/openthread,nibanks/openthread,pvanhorn/openthread,JakubBrachTieto/openthread,lanyuwen/openthread,nibanks/openthread,gandreello/openthread,bukepo/openthread,srickardti/openthread,turon/openthread,aeliot/openthread,fbsder/openthread,bukepo/openthread,erja-gp/openthread,abtink/openthread,srickardti/openthread,mszczodrak/openthread,jwhui/openthread,nibanks/openthread,vaas-krish/openthread,jjlee3/openthread,abtink/openthread,GiedriusM/openthread,openthread/openthread,fbsder/openthread