socket: fix assertion in nl_connect() when all ports are already in use

socket: fix assertion in nl_connect() when all ports are already in use

When generating a port fails a few times (because they are already in used
outside of libnl's knowledge), we would back off generating a local
port and instead let kernel decide.

There was however a bug in nl_connect() that caused an assertion:

    BUG at file position socket.c:147:_nl_socket_used_ports_release_all
    app: socket.c:147: _nl_socket_used_ports_release_all: Assertion `0' failed.

Fixes: 96e1e5bdc2e803700055395cc3c428fa2525d1ca