dhclient: Ignore vendor-identifying DHCP options defined in RFC 3925

Ignore DHCP options 124 and 125 to shut up the warning messages.
These options are defined in the RFC 3925.

PR: 281361
Reviewed by: jrm (mentor), otis (mentor), thj
Tested by: jlduran@gmail.com
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D46760

(cherry picked from commit 38c63b52830c85013f30bc62b2b32f3936d84e65)