ubus: fix ubus announcements txt fields

ubus: fix ubus announcements txt fields

The txt field of multicast dns is defined as an array of concatenated
length-values, where length is encoded in the first byte and value is a
non-NUL terminated string.
The ubus announcements callback tokenized the txt buffer by dividing
it between non-ASCII characters. This works fine for values with a
length <32 characters, but not for longer strings.
This patch correctly deserializes the txt values and removes the need
for dynamic allocation.

Signed-off-by: Andrew Karpow <[email protected]>
Signed-off-by: Felix Fietkau <[email protected]> [minor cleanup]