NFSv4: limit lease period in nfs4_set_lease_period()

NFSv4: limit lease period in nfs4_set_lease_period()

In nfs4_set_lease_period(), the passed 32-bit lease period in seconds is
multiplied by HZ -- that might overflow before being implicitly cast to
*unsigned long* (32/64-bit type), while initializing the lease variable.
Cap the lease period at MAX_LEASE_PERIOD (#define'd to 1 hour for now),
before multipying to avoid such overflow...

Found by Linux Verification Center (linuxtesting.org) with the Svace static
analysis tool.

Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Suggested-by: Trond Myklebust <trondmy@kernel.org>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>