This replaces deprecated backticks by more versatile $(...) syntax.
This does not touch lib/upgrade/nand.sh, as there replacement is
not trivial.
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
uci-defaults are sourced and non-executable, so they do not require
a shebang.
While at it, apply consistent naming scheme.
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>