It can easily happen that the generated local netlink port is alrady in
use. In that case bind will fail with ADDRINUSE.
Users of libnl3 could workaround this, by managing the local ports
themselves, but sometimes these users are libraries too and they also
don't know which ports might be used by other components.
This patch changes that nl_socket_alloc() no longer initilizes the local
port id immediately. Instead it will be initialized when the user calls
nl_socket_get_local_port() the first time and thereby shows interest in
the value.
If bind() fails with ADDRINUSE, check if the user ever cared about the
local port, i.e. whether the local port is still unset. If it is still
unset, assume that libnl should choose a suitable port and retry until
an unused port can be found.
Signed-off-by: Thomas Haller <thaller@redhat.com>
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