rds: Fix inaccurate accounting of unsignaled wrs

The number of unsignaled work-requests posted to the IB send queue is
tracked by a counter in the rds_ib_connection struct. When it reaches
zero, or the caller explicitly asks for it, the send-signaled bit is
set in send_flags and the counter is reset. This is performed by the
rds_ib_set_wr_signal_state() function.

However, this function is not always used which yields inaccurate
accounting. This commit fixes this, re-factors a code bloat related to
the matter, and makes the actual parameter type to the function
consistent.

Signed-off-by: Håkon Bugge <haakon.bugge@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>