Rx: avoid lock churn in rxi_ReceiveAckPacket

Rx: avoid lock churn in rxi_ReceiveAckPacket

rxi_ReceiveAckPacket can acquire and drop the conn_data_lock several
times and acquires and drops the peer_lock unnecessarily.  This patchset
adds a variable to track whether the conn_data_lock is held in order
to avoid the need to drop it and reacquire it based upon conditional
operations.  It also relocates the peer->maxPacketSize computations
in order to consolidate the work performed under the peer_lock.

Change-Id: I0bc9e42e8ef198a04315f9f2df529073ce9dfd03
Reviewed-on: http://gerrit.openafs.org/2781
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>