staging: lustre: fixup kernel Kconfig option LNET_MAX_PAYLOAD

A few errors exist for the Kconfig option LNET_MAX_PAYLOAD. First
mistake is the default size is 1MB not 2MB as it is shown to the
person configuring the kernel. Second the LNET_MAX_PAYLOAD option
is more closely related to LNET than the LUSTRE_FS option.

Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>