v2.10.0

uspot: portal: avoid null dereference, always define ctx.ssid

This commit fixes a bug where the SSID value would be set to "unknown"
in spotfilter data when the hostapd call returned without SSID data; but
this value  was not propagated internally, resulting in a null value
being used in other parts of the portal code. Furthermore, if the
hostapd call returned null data, the spotfilter assignment correctly
handled this case but not the subsequent internal assignment, resulting
in a potential null dereference and crash.

Signed-off-by: Thibaut VARÈNE <hacks@slashdirt.org>