[SCTP]: Honor flags when setting peer address parameters

Parameters only take effect when a corresponding flag bit is set
and a value is specified. This means we need to check the flags
in addition to checking for non-zero value.

Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>