package/fastd: propagate libcap dependency

libcap neds headers >= 3.0, so propagate that down to fastd which
selects libcap.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Alexander Dahl <post@lespocky.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>