IB/qib: Clear eager buffer memory for each new process

The eager buffers are not being cleared before being mmapped into a
new user address space.  This is a potential security risk and should
be fixed.  Note that the eager header queue is already being cleared.

Signed-off-by: Ralph Campbell <ralph.campbell@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>