RDMA/nes: Fix up nes_lro_max_aggr module parameter

Fix some bugs with the max_aggr module parameter added with LRO support:

 - The module parameter value ignored and not actually used to set
   lro_mgr.max_aggr.
 - MODULE_PARM_DESC had a typo "_mro_" instead of "_lro_" so it didn't
   end up describing the actual module parameter.
 - The nes_lro_max_aggr variable was declared as unsigned, but the
   module_param line said "int" instead of "uint" for the type.
 - The default value for the parameter was stuck in the permissions
   field of module_param, which led to nonsensical permissions for the
   file under /sys/module/iw_nes/param.
 - The parameter was used in only one file but defined in another, which
   led to the variable being global for no good reason.  Move everything
   related to the parameter to the file nes_hw.c where it is actually
   used.

Signed-off-by: Roland Dreier <rolandd@cisco.com>