nfscommon: Update the nfs_bigreply array

The variable is simply a long series of flags. Mark as boolean to allow
the compiler to use smaller types.

Convert to designated initializer to better indicate which operations it
is set for. Without this the array is kind of long and sparse.

nfsv4_setsequence() is no longer used outside nfs_commonsubs.c, so now
mark it as static. The fourth argument is true/false, so convert to
boolean.

No semantics change is made by this commit.

Discussed with: jrtc27
MFC after: 2 weeks