dhcp/dhclient: Improve "interface" statement parsing
In commit d405cfd9089f9552969e6a3e1a1c4550fc3c1695, parsing "interface"
statement is introduced. But it leads to uncommplete parsing of the
"request" entry, if one of the lines in "request" entry is prefixed with
word "interface". For example, the default configuration of openSUSE
distribution:
request subnet-mask, broadcast-address, routers,
rfc3442-classless-static-routes,
interface-mtu, host-name, domain-name, domain-search,
domain-name-servers, nis-domain, nis-servers,
nds-context, nds-servers, nds-tree-name,
netbios-name-servers, netbios-dd-server,
netbios-node-type, netbios-scope, ntp-servers;
Fixes commit d405cfd9089f9552969e6a3e1a1c4550fc3c1695.
