sunrpc: set SOCK_FASYNC

sunrpc is using SOCKWQ_ASYNC_NOSPACE without setting SOCK_FASYNC,
so the recent optimizations done in sk_set_bit() and sk_clear_bit()
broke it.

There is still the risk that a subsequent sock_fasync() call
would clear SOCK_FASYNC, but sunrpc does not use this yet.

Fixes: 9317bb69 ("net: SOCKWQ_ASYNC_NOSPACE optimizations")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Jiri Pirko <jiri@resnulli.us>
Reported-by: Huang, Ying <ying.huang@intel.com>
Tested-by: Jiri Pirko <jiri@resnulli.us>
Tested-by: Huang, Ying <ying.huang@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>