The giant size of the TCP proc struct is causing a problem in some
environments (because it is allocated on the stack), and it was too
big, anyway.
Instead, use a hash map. That way, it starts small and can grow if it
needs to. It also makes no assumptions about the values of the kernel
interface indexes.
Fixes#5292.
Signed-off-by: Jeff Squyres <jsquyres@cisco.com>