lib: reject leading 0 in ipv4 decimal quad

lib: reject leading 0 in ipv4 decimal quad

inet_pton() is used to parse ipv4 addresses internally, therefore FRR
does not support octal notation for quads. The ipv4 cli token validator
should make sure that str2prefix() can parse tokens it allows, and
str2prefix uses inet_pton, so we have to disallow leading zeros in ipv4
quads.

In short, 1.1.1.01 is no longer valid and must be expressed as 1.1.1.1.

Signed-off-by: Quentin Young <qlyoung@cumulusnetworks.com>