ipwireless: Increase PPP outgoing queue size

Increase default size of PPP outgoing queue. Currently set to 1, which
means that a packet quickly following another pushed by PPP must wait
until hardware actually sends the previous and PPP has to be waken up
by ppp_wakeup(). This slows down upstream.

Now PPP can push more packets at once which get buffered inside driver
and pushed immediatelly to hardware when previous packet is out.

Experiments show that size = 10 is quite good for all connection types
(GPRS/EDGE/UMTS) and gains 4 KB/sec of upload for UMTS for batch uploads.
Need for higher queue size than 10 occures in only < 0.1 % of cases.
Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>