MFC r202289:

MFC r202289:

  Reject invalid CIDR widths rather than silently stopping at the first
  non-digit character.

  Due to an issue with rc(8) in a test configuration, ifconfig was being
  invoked with the address used again as the width - for example,

    ifconfig vlan0 10.0.0.1/10.0.0.1

  Prior to this change, that address/width would be interpreted as
  10.0.0.1/10.

git-svn-id: svn://svn.freebsd.org/base/stable/8@212114 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f