ldpd: fix bug when changing the transport address

ldpd: fix bug when changing the transport address

When the transport address is changed, all interfaces and targeted
neighbors are temporary disabled in the ldpe process until new sockets
bound to the new transport address are received from the parent.

This patch fixes a problem in which adjacencies weren't being removed
after the associated targeted neighbors were disabled. This was causing
ldpd not to set some MD5 sockoptions for new neighbors are thus preventing
MD5-protected sessions to come up after a change in the transport-address.

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>