BB: hostapd: Fix RADIUS connection recovery after initial failure (#18197)

If the initial attempt at opening the socket connection to the RADIUS
server failed due to missing IP connectivity during startup, e.g., with
"connect[radius]: Network is unreachable", hostapd did not try to
reconnect when RADIUS messages were sent. Instead, it only reported "No
authentication server configured" even if the configuration did have a
server entry.

Backport of upstream commit 94b39e5927e570e6b0fe41d455dde0a361c71c36
("RADIUS client: Fix server connection recovery after initial failure")

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>
git-svn-id: svn://svn.openwrt.org/openwrt/branches/barrier_breaker@46512 3c298f89-4303-0410-b956-a3cf2f4a3e73