IB/ipoib: Add handling for sending of skb with many frags

IB/ipoib: Add handling for sending of skb with many frags

Orabug: 21498734

IPoIB puts skb-fragments in SGEs adding 1 extra SGE when SG is enabled.
Current codepath assumes that the max number of SGEs a device supports
is at least MAX_SKB_FRAGS+1, there is no interaction with upper layers
to limit number of fragments in an skb if a device suports fewer SGEs.
The assumptions also lead to requesting a fixed number of SGEs when
IPoIB creates queue-pairs with SG enabled.

A fallback/slowpath is implemented using skb_linearize to
handle cases where the conversion would result in more sges than supported.

Change-Id: Ia81e69d7231987208ac298300fc5b9734f193a2d
Signed-off-by: Hans Westgaard Ry <hans.westgaard.ry@oracle.com>
Reviewed-by: Håkon Bugge <haakon.bugge@oracle.com>
Reviewed-by: Wei Lin Guay <wei.lin.guay@oracle.com>