dpif: Fix slow action handling for DP_HASH and RECIRC

In case DP_HASH and RECIRC actions need to be executed in slow path,
current implementation simply don't handle them -- vswitchd simply
crashes. This patch fixes them by supply an implementation for them.

RECIRC will be handled by the datapath, same as the output action.

DP_HASH, on the other hand, is handled in the user space. Although the
resulting hash values may not match those computed by the datapath, it
is less expensive; current use case (bonding) does not require a strict
match to work properly.

Reported-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Signed-off-by: Andy Zhou <azhou@nicira.com>
Acked-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>