dhcp: Compare DIUD_LL as a network short

dhcp: Compare DIUD_LL as a network short

The existing comparision triggers the following clang assertion:

    error: result of comparison of constant 50331648 with expression of type
    'u16' (aka 'unsigned short') is always true

Section 9.1 of RFC3315 describes the DUID type field as:
    "A DUID consists of a two-octet type code represented in network byte"

correctly convert the local type to a network short for the comparison.

Type: fix
Change-Id: I7cb048035bd5e06372e29471ae6004ee1b2191b9
Signed-off-by: Tom Jones <thj@freebsd.org>