src/jit.rs: Move emitting functions to JitCompiler

These functions belong to the JIT compiler and should be part of its
implementation.

Also, remove the [#inline] directives: I can't remember what they were
here for in the first place, possibly just because uBPF would inline the
equivalent functions. Leave it to the compiler to decide what to inline.

Signed-off-by: Quentin Monnet <quentin@isovalent.com>