Don't drop a reference to the TOE PCB in undo_offload_socket().

undo_offload_socket() is only called by t4_connect() during a connection
setup failure, but t4_connect() still owns the TOE PCB and frees ita
after undo_offload_socket() returns. Release a reference in
undo_offload_socket() resulted in a double-free which panicked when
t4_connect() performed the second free. The reference release was
added to undo_offload_socket() incorrectly in r299210.

MFC after: 1 week
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