Add SRQ support to userspace verbs module.  This adds several commands
and associated structures, but it's OK to do this without bumping the
ABI version because the commands are added at the end of the list so
they don't change the existing numbering.  There are two cases to
worry about:

1. New kernel, old userspace.  This is OK because old userspace simply
   won't try to use the new SRQ commands.  None of the old commands are
   changed.

2. Old kernel, new userspace.  This works perfectly as long as
   userspace doesn't try to use SRQ commands.  If userspace tries to
   use SRQ commands, it will get EINVAL, which is perfectly
   reasonable: the kernel doesn't support SRQs, so we couldn't do any
   better.
Signed-off-by: Roland Dreier <rolandd@cisco.com>