Update ganeti-os-interface documentation
Update ganeti-os-interface documentation

man/ganeti-os-interace.sgml lacked complete information for the NIC-related
environment variables. Added a reference to NIC_%N_LINK and NIC_%N_MODE and
clarified the reference to NIC_%N_BRIDGE.

Signed-off-by: Apollon Oikonomopoulos <2346bd49f3482f908ee2692e0cc8970349c7870a@noc.grnet.gr>
Signed-off-by: Iustin Pop <acf83a5274f31a43af6b914614365999469c1a31@google.com>
Reviewed-by: Iustin Pop <acf83a5274f31a43af6b914614365999469c1a31@google.com>

grnet/snf-ganeti,ganeti-github-testing/ganeti-test-1,onponomarev/ganeti,yiannist/ganeti,mbakke/ganeti,ganeti/ganeti,apyrgio/snf-ganeti,mbakke/ganeti,apyrgio/ganeti,leshchevds/ganeti,onponomarev/ganeti,apyrgio/ganeti,leshchevds/ganeti,ganeti/ganeti,andir/ganeti,dimara/ganeti,grnet/snf-ganeti,leshchevds/ganeti,andir/ganeti,andir/ganeti,ganeti-github-testing/ganeti-test-1,mbakke/ganeti,yiannist/ganeti,bitemyapp/ganeti,dimara/ganeti,ganeti/ganeti,apyrgio/snf-ganeti,bitemyapp/ganeti,yiannist/ganeti