msm: rndis_ipa: set packet limit to 1 for downlink aggregation

This commit is for the cases were Hosts
requests small aggregation limit in downlink path.
Depends on how small the request is, the IPA core
aggregation byte limit can be set to 0.
Setting 0 as byte limit causes the IPA core to wait for
time limit or packet limit which causes great latency
and even impact throughput for device to host path.
This change make sure that the packet limits is used with
the value 1.

Change-Id: I530e3025d827cd0712a9daf91aaacae4981792d3
Signed-off-by: Talel Shenhar <tatias@codeaurora.org>