bnxt_en: Fix TQM fastpath ring backing store computation

TQM fastpath ring needs to be sized to store both the requester
and responder side of RoCE QPs in TQM for supporting bi-directional
tests.  Fix bnxt_alloc_ctx_mem() to multiply the RoCE QPs by a factor of
2 when computing the number of entries for TQM fastpath ring.  This
fixes an RX pipeline stall issue when running bi-directional max
RoCE QP tests.

Fixes: c7dd7ab4

 ("bnxt_en: Improve TQM ring context memory sizing formulas.")
Signed-off-by: Rukhsana Ansari <rukhsana.ansari@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>