nfs: fix dead code of ipv6_addr_scope

The correct way to check on IPV6_ADDR_SCOPE_LINKLOCAL is to check with
the ipv6_addr_src_scope function.

Currently this can't be work, because ipv6_addr_scope returns a int with
a mask of IPV6_ADDR_SCOPE_MASK (0x00f0U) and IPV6_ADDR_SCOPE_LINKLOCAL
is 0x02. So the condition is always false.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>