Fix spurious white space introduced in r301059

r301059 accidently introduced a subtle change for point to point interfaces
where an extra space is inserted before the netmask. This can cause issues
for scripts that parse ifconfig output.

Submitted by: Kevin Bowling <kevin.bowling@kev009.com>
Reviewed by: hiren
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D8199