net: 6lo: Fix 6lo uncompression issue

When source address is unspecified then SAC is 1 and SAM is 00.
Uncompression does not process because context based compression
is not enabled.
Special case (SAC:1 and SAM:00) should be handled without context
based compression support.

Signed-off-by: Ravi kumar Veeramally <ravikumar.veeramally@linux.intel.com>