treewide: replace which with command -v

Fix shellcheck SC2230
> which is non-standard. Use builtin 'command -v' instead.

Once applied to everything concerning OpenWrt we can disable the busybox
feature `which` and save 3.8kB.

Signed-off-by: Paul Spooren <mail@aparcar.org>

utils/lxc/patches/020-lxc-checkconfig.patch

@@ -7,7 +7,7 @@
 +: ${ZGREP:=zgrep}
 +: ${GUNZIP:=gunzip}
 +
-+if [ -z $(which $ZGREP) ] && ! [ -z $(which $GUNZIP) ] && [ -x $(which $GUNZIP) ] &&  [ -f $CONFIG ] && [ "$CONFIG" == "/proc/config.gz" ] ; then
++if [ -z $(command -v $ZGREP) ] && ! [ -z $(command -v $GUNZIP) ] && [ -x $(command -v $GUNZIP) ] &&  [ -f $CONFIG ] && [ "$CONFIG" == "/proc/config.gz" ] ; then
 +
 +	CONFIG_NEW="/tmp/config-$(uname -r)"
 +	$GUNZIP -c $CONFIG > $CONFIG_NEW