NFS: Convert use of __constant_htonl to htonl

In little endian cases, the macro htonl unfolds to __swab32 which
provides special case for constants. In big endian cases,
__constant_htonl and htonl expand directly to the same expression.
So, replace __constant_htonl with htonl with the goal of getting
rid of the definition of __constant_htonl completely.

The semantic patch that performs this transformation is as follows:

@@expression x;@@

- __constant_htonl(x)
+ htonl(x)

Signed-off-by: Vaishali Thakkar <vthakkar1994@gmail.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>