speexdsp: New package required for build of tshark-4.2.5

speexdsp: New package required for build of tshark-4.2.5

- tshark in the past had its own version of speexdsp used only for some "arbitrary
   resampling code" used for the build of tshark.
- speexdsp has been removed from tshark so it is now a build requirement.
- It is only used for the build of tshark so the rootfile has all entries commented out.

Tested-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>