net: ice: Fix potential NULL pointer dereference in ice_bridge_setlink()

In the Linux kernel, the following vulnerability has been resolved: net: ice: Fix potential NULL pointer dereference in ice_bridge_setlink() The function ice_bridge_setlink() may encounter a NULL pointer dereference if nlmsg_find_attr() returns NULL and br_spec is dereferenced subsequently in nla_for_each_nested(). To address this issue, add a check to ensure that br_spec is not NULL before proceeding with the nested attribute iteration.