router: fix lingering uloop socket descriptor

router: fix lingering uloop socket descriptor

In case setting one of the socket options fails; make sure the raw
socket is removed from the uloop file descriptor list before the
socket is closed.
In case this is not done and a new raw socket is created with the
same fd value odhcpd will not be triggered by uloop in case RS messages
are received on the socket as reported in https://github.com/openwrt/odhcpd/issues/135

Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>