Fix min/max macros in include/common.h

There is a bug in the min and max macros in common.h which occurs if
Y is a larger type than X. For example, if Y is a 64-bit value and X
is a 32-bit value then Y will be truncated to 32-bits.  This fix
matches what is done in the Linux kernel but without the additional
type checking present in the kernel version.

Signed-off-by: Aaron Williams <aaron.williams@caviumnetworks.com>