Fix a tvb memory leak;

Fix a tvb memory leak;
  Essentially: generate tvbuffs as needed; don't save them for later reuse
               with the result they are never freed.

Also:
- move a struct from packet-nfs.h to packet-nfs.c since it's only used locally;
- reformat some long lines.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@40205 f5534014-38df-0310-8fa8-9805f1628bb7