ch4/ofi: default MPIR_CVAR_CH4_OFI_EAGER_THRESHOLD to -1

Set default MPIR_CVAR_CH4_OFI_EAGER_THRESHOLD to -1 so we prefer
libfabric native path rather than mpich-layer forced rndv.

This was the intention but got neglected during merge.

Author: hzhou

src/mpid/ch4/netmod/ofi/ofi_send.h

@@ -40,7 +40,7 @@
     - name        : MPIR_CVAR_CH4_OFI_EAGER_THRESHOLD
       category    : CH4_OFI
       type        : int
-      default     : 16384
+      default     : -1
       class       : none
       verbosity   : MPI_T_VERBOSITY_USER_BASIC
       scope       : MPI_T_SCOPE_LOCAL