main/busybox: enable chattr/lsattr

chattr is useful for all sort of filesystems and is by no mean ext specific:
+i, +a (immutable/append only) work on many filesystems,
+C (nocow) also apply to btrfs etc etc

Size difference by enabling it are:
Original size:
apk size 502641
installed bin/busybox size 837272

chattr:
apk size 503578 (+937)
installed bin/busybox size 837272 (+0)

chattr and lsattr:
apk size 504505 (+927)
installed bin/busybox size 837272 (+0)

(yes, you're reading that right, the installed size does not change
except for the creation of two symlinks. The text/bss sizes change
a bit, but it all fits in existing padding)

For comparison, e2fsprogs-extra (the 'real' chattr) has a
footprint of about 2MB that I'd like to avoid (installed on embedded
device with limited size),
and adding it to busybox-extras has
apk size 53827 / 57159 (+3332) / 57953 (+794)
installed bin/busybox-extra size 104072 / 108168 / 108168
so there is less advantageous, but still tiny so I'd be happy either way.

thanks!