NFS has 3 settings in Lion Server: nbDaemons, the number of NFS daemons, useTCP, whether or not TCP is used and useUDP, whether or not udp is used. To disable UDP forces TCP:
serveradmin settings nfs:useUDP = 0
Or to turn UDP back on:
serveradmin settings nfs:useUDP = 1
To disable TCP if you’d rather just use UDP:
serveradmin settings nfs:useTCP = 0
Or to turn TCP back on:
serveradmin settings nfs:useTCP = 1
