sdlog2: getopt invalid usage fixed
sdlog2: use orb_check() instead of poll() to minimize polling overhead, bugs and compiler warnings fixed
sdlog2: code style fixed
Merge branch 'master' into sdlog2_opt
sdlog2: move some global variables to local scope, set default log rate to 50 Hz
sdlog2: lseek() workaround removed
sdlog2: bug fixed, sleep when idle too
sdlog2: max write chunk increased to 1024
Revert "sdlog2: max write chunk increased to 1024"

This reverts commit a478dac621301a993fb8ed13b86abd61d93bfec0.
Merge branch 'getopt_fixes' into sdlog2_opt
Merge branch 'master' into sdlog2_opt
Merge pull request #711 from PX4/sdlog2_opt

sdlog2 optimization