[XFS] Move xfs_attr_rolltrans to xfs_trans_roll

Move it from the attr code to the transaction code and make
the attr code call the new function.

We rolltrans is really usefull whenever we want to use rolling
transaction, should be generic, it isn't dependent on any part
of the attr code anyway.

We use this excuse to change all the:

if ((error = xfs_attr_rolltrans()))

calls into:

error = xfs_trans_roll();

if (error)

SGI-PV: 981498

SGI-Modid: xfs-linux-melb:xfs-kern:31729a

Signed-off-by: Niv Sardi <xaiki@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>