Make osi_fetchstore.c protocol independent

Make osi_fetchstore.c protocol independent

For future use of OSD and vicep-access osi_fetchstore.c should not depend on
the rx-fileserver-protocol but call instead the routines pointed to by ops.

Some code beautyfication in afs_fetchstore.c to use nBytes instead of code.

New global variable afs_protocols in afs_fetchstore.c which will be used
in RXOSD/VICEP-ACCESS programs in the future.

Change-Id: Id6b6e6c794b4fb00ad4719670caefd381f98949b
Reviewed-on: http://gerrit.openafs.org/2952
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>