[PATCH libosmocore] doxyfiles: refer paths to @srcdir@

[Sylvain Munaut]

> When building out-of-srcdir, paths such as "src/gsm" will not find any
> source files.  Since the Doxyfiles are preprocessed, we can prepend
> @srcdir@ to fix that.
>
> Signed-off-by: Alex Badea <vamposdecampos at gmail.com>

Merged.

Also applied an equivalent patch to libosmo-dsp.

If anyone has created a Doxy template following the examples in
libosmocore, you might want to check if that fix is required as well.

Cheers,

   Sylvain