Fix strict compile build breakage in svc_dg.c

sa_family member variable of struct sockaddr has different data types based on
_USE_BSD switch. Initializing sa_family with 0xffff implicitely truncates the
value where data type is uint8. Later comparison (sp->sa_family == 0xffff) will
always be false due to implicit truncation of the value.
We can safely initialize it with 0xff to avoid this situation.

Signed-off-by: Sachin Bhamare <sbhamare@panasas.com>