fix unused_assignments warning

[johann-cm]

cargo test was reporting a warning on unused assignments on e3:

error: value assigned to `e3` is never read
Error:    --> libuci-sys/src/lib.rs:217:9
    |
217 |         e3.list.prev = &raw mut e2.list;
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: maybe it is overwritten before being read?
    = note: `-D unused-assignments` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(unused_assignments)]`

error: value assigned to `e3` is never read
Error:    --> libuci-sys/src/lib.rs:218:9
    |
218 |         e3.list.next = &raw mut head;
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: maybe it is overwritten before being read?

error: value assigned to `e3` is never read
Error:    --> libuci-sys/src/lib.rs:219:9
    |
219 |         e3.type_ = 3;
    |         ^^^^^^^^^^^^
    |
    = help: maybe it is overwritten before being read?

I guess the compiler does not understand the linked list with raw pointers very well.
Technically, only e3 needed to be renamed, but I renamed e1, e2, e3 for consistency.