SUNRPC: Cache deferral injection

Cache deferral injection stress-tests the cache deferral logic as
well as upper layer protocol deferred request handlers. This
facility is for developers and professional testers to ensure
coverage of the rqst deferral code paths. To date, we haven't
had an adequate way to ensure these code paths are covered
during testing, short of temporary code changes to force their
use.

A file called /sys/kernel/debug/fail_sunrpc/ignore-cache-wait
enables administrators to disable cache deferral injection while
allowing other types of sunrpc errors to be injected. The default
setting is that cache deferral injection is enabled (ignore=false).

To enable support for cache deferral injection,
CONFIG_FAULT_INJECTION, CONFIG_FAULT_INJECTION_DEBUG_FS, and
CONFIG_SUNRPC_DEBUG must all be set to "Y".

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

SUNRPC: Server-side disconnect injection

Disconnect injection stress-tests the ability for both client and
server implementations to behave resiliently in the face of network
instability.

A file called /sys/kernel/debug/fail_sunrpc/ignore-server-disconnect
enables administrators to turn off server-side disconnect injection
while allowing other types of sunrpc errors to be injected. The
default setting is that server-side disconnect injection is enabled
(ignore=false).

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

SUNRPC: Move client-side disconnect injection

Disconnect injection stress-tests the ability for both client and
server implementations to behave resiliently in the face of network
instability.

Convert the existing client-side disconnect injection infrastructure
to use the kernel's generic error injection facility. The generic
facility has a richer set of injection criteria.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

SUNRPC: Add a /sys/kernel/debug/fail_sunrpc/ directory

This directory will contain a set of administrative controls for
enabling error injection for kernel RPC consumers.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>