Refactor struct transport_ops inlined into struct transport

Refactor struct transport_ops inlined into struct transport

Aside from reducing the code by 20 lines this refactoring removes
a level of indirection when trying to access the operations of a
given transport "instance", making the code clearer and easier to
follow.

It also has the nice effect of giving us the benefits of C99 style
struct initialization (namely ".fetch = X") without requiring that
level of language support from our compiler.  We don't need to worry
about new operation methods being added as they will now be NULL'd
out automatically by the xcalloc() we use to create the new struct
transport we supply to the caller.

This pattern already exists in struct walker, so we already have
a precedent for it in Git.  We also don't really need to worry
about any sort of performance decreases that may occur as a result
of filling out 4-8 op pointers when we make a "struct transport".
The extra few CPU cycles this requires over filling in the "struct
transport_ops" is killed by the time it will take Git to actually
*use* one of those functions, as most transport operations are
going over the wire or will be copying object data locally between
two directories.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>