exportfs: reallow building as a module

exportfs: reallow building as a module

Commit a070de25562c3f5d5f413624cdf3143ea7361207 ("vfs: Add name to file
handle conversion support") changed EXPORTFS to be a bool.
This was needed for earlier revisions of the original patch, but the actual
commit put the code needing it into its own file that only gets compiled
when FHANDLE is selected which in turn selects EXPORTFS.
So EXPORTFS can be safely compiled as a module when not selecting FHANDLE.

Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Acked-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>