V7.1 Ptf SI46878 was the PTF that had the TCP support for NFS.
Check the cover letter for details, but here is a snip.
CORRECTION FOR APAR SE52046 :
Support has been added to allow the IBM i NFS client to use the
TCP protocol for communication with NFS file servers. While use
of the UDP protocol remains the default, a user may choose to
enable the TCP support by issuing the following command:
CALL QP0FPTOS (*NFSFORCE UDP OFF)
This setting does not persist when the system is restarted, so
it is advisable to add the command to the start-up program
before any NFS mounts are established if use of TCP is desired.