dhclient: Ignore SIP servers DHCP option defined in RFC 3361

Ignore SIP servers dhcp option to shut up the warning message.
This option is defined in the RFC 3361 and sent from NSD-G1000T router.

PR: 280119
Reviewed by: jrm (mentor), brooks
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D45873

(cherry picked from commit ac6dc5cde729a602252a0b80f82424861d2eb7b5)