rust: fix mismatched_lifetime_syntaxes warning

rust: fix mismatched_lifetime_syntaxes warning

Fix new warning present in Rust 1.89, for example:

warning: hiding a lifetime that's elided elsewhere is confusing
   --> src/ike/parser.rs:295:30
295 | pub fn parse_key_exchange(i: &[u8], length: u16) -> IResult<&[u8], KeyExchangePayload> {
    = help: the same lifetime is referred to in inconsistent ways, making the signature confusing