Add DHCP client dict for physical interfaces

[duanetoler]

Add DHCP dict to physical interface module argument fields Update documentation accordingly

[duanetoler]

Tested on R81.20 JHF 26 and JHF 41 Configuration is written to CLISH and /etc/dhclient.conf, dhclient starts and runs as expected.

[chkp-majds]

will push this as part of another commit