nfsd4: keep per-session list of connections

The spec requires us in various places to keep track of the connections
associated with each session.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

diff --cc fs/nfsd/nfs4state.c
Simple merge

diff --cc fs/nfsd/state.h
Simple merge

diff --cc include/linux/nfs4.h
Simple merge