fuse: Freeze client on suspend when request sent to userspace

Suspend attempts can abort when the FUSE daemon is already frozen
and a client is waiting uninterruptibly for a response, causing
freezing of tasks to fail.

Use the freeze-friendly wait API, but disregard other signals.

Change-Id: Icefb7e4bbc718ccb76bf3c04daaa5eeea7e0e63c
Signed-off-by: Todd Poynor <toddpoynor@google.com>