usnic: reduce sizeof(ompi_btl_usnic_addr_t) to 56 bytes

Trivial struct re-ordering to eliminate holes in the middle of the
struct (although there's still a hole at the end) and reduce the
overall size of the struct from 64 to 56 bytes.  Also change mtu from
int to uint16_t; there was no need for it to be that large.

Reviewed by Dave Goodell

cmr=v1.8.2:reviewer=ompi-rm1.8

This commit was SVN r31688.

ompi/mca/btl/usnic/btl_usnic_endpoint.h

@@ -65,15 +65,15 @@ typedef enum ompi_btl_usnic_channel_id_t {
 } ompi_btl_usnic_channel_id_t;
 
 typedef struct ompi_btl_usnic_addr_t {
-    ompi_btl_usnic_seq_t isn;
-    uint32_t qp_num[USNIC_NUM_CHANNELS];
     union ibv_gid gid;
+    uint32_t qp_num[USNIC_NUM_CHANNELS];
     uint32_t ipv4_addr;
     uint32_t cidrmask;
     uint32_t connectivity_udp_port;
-    uint8_t mac[6];
-    int mtu;
     uint32_t link_speed_mbps;
+    uint16_t mtu;
+    ompi_btl_usnic_seq_t isn;
+    uint8_t mac[6];
 } ompi_btl_usnic_addr_t;
 
 struct ompi_btl_usnic_send_segment_t;

ompi/mca/btl/usnic/btl_usnic_proc.c

@@ -602,7 +602,7 @@ static int match_modex(ompi_btl_usnic_module_t *module,
      * the min of the two MTUs?  Another choice is to disqualify this pairing
      * before running the matching algorithm on it. */
     if (*index_out >= 0 &&
-        proc->proc_modex[*index_out].mtu != module->if_mtu) {
+        proc->proc_modex[*index_out].mtu != (uint16_t) module->if_mtu) {
         opal_show_help("help-mpi-btl-usnic.txt", "MTU mismatch",
                     true,
                     ompi_process_info.nodename,