net: qmi_wwan: increase max QMI message size to 4096

net: qmi_wwan: increase max QMI message size to 4096

QMI requests exceeding 1500 bytes are possible and
device firmware does not handle fragmented messages
very well.  It is therefore necessary to increase
the maximum message size from the current 512 bytes.

The protocol message size limit is not documented
in any publicly known source, but the out of tree
driver from CodeAurora use 4 kB.  This is therefore
chosen as the new arbitrary default until the real
limit is known.

This should allow any QMI message to be transmitted
without fragmentation, fixing known issues with GPS
assistance data upload.

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>