build: Rework how MULTIPATH_NUM is delivered to build

Changes made here:

1) MULTIPATH_NUM will never be 0.  If user specifies --enable-multipath=0
then this translates to MULTIPATH_NUM being set to 64 inside of the build
system.

2) Move MULTIPATH_NUM from a Makefile construct to a config.h construct.

3) Allowed MULTIPATH_NUM to be a number > 99 but < 1000

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>
3 files changed