quagga: fix build when ospfd is disabled

quagga: fix build when ospfd is disabled

ospfclient and ospfapi that gets build by default need libospf, but libospf
doesn't get built when ospfd is disabled. Disable ospfapi in this case.

Fixes:
http://autobuild.buildroot.net/results/918/918f5ced9c7dd59a8fcab654dc8f6d2798515e34/
http://autobuild.buildroot.net/results/edb/edbcb616b6019bced330238228fb5c6f880ab885/
http://autobuild.buildroot.net/results/831/8311f611559b3e7e98860d5a0264db97d4de1a54/

and many more.

[Peter: tweak description]
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>