sane-backends: select all backends when CONFIG_ALL

sane-backends: select all backends when CONFIG_ALL

sane-xxx backend packages are hidden packages with custom
config and CONFIG_ALL does not select them alone. Now
sane-backends depends on +ALL:sane-backends-all.

No existing ipk is affected as the changed package/sane-backends
does not exist as an ipk.

030-musl.patch was updated to be submitted upstream. However,
the added preprocessor #if are always true for OpenWRT and will
not change the resulting code.

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>