base-files: add functions to set or clear bit in MAC address

Some devices (e.g. Arduino Yun) need bitwise operations during MAC address
setup. This commit adds generalized versions of macaddr_setbit_la(), which
are helpful when manipulating a single bit in a MAC address.

Signed-off-by: Sungbo Eo <mans0n@gorani.run>

package/base-files/files/lib/functions/system.sh

@@ -152,10 +152,26 @@ macaddr_geteui() {
 	echo ${mac:9:2}$sep${mac:12:2}$sep${mac:15:2}
 }
 
-macaddr_setbit_la() {
+macaddr_setbit() {
 	local mac=$1
+	local bit=${2:-0}
 
-	printf "%02x:%s" $((0x${mac%%:*} | 0x02)) ${mac#*:}
+	[ $bit -gt 0 -a $bit -le 48 ] || return
+
+	printf "%012x" $(( 0x${mac//:/} | 2**(48-bit) )) | sed -e 's/\(.\{2\}\)/\1:/g' -e 's/:$//'
+}
+
+macaddr_unsetbit() {
+	local mac=$1
+	local bit=${2:-0}
+
+	[ $bit -gt 0 -a $bit -le 48 ] || return
+
+	printf "%012x" $(( 0x${mac//:/} & ~(2**(48-bit)) )) | sed -e 's/\(.\{2\}\)/\1:/g' -e 's/:$//'
+}
+
+macaddr_setbit_la() {
+	macaddr_setbit $1 7
 }
 
 macaddr_2bin() {