Re-enabling collective operations using SHMEM

Due to error on one of the regtests were disabled in the previous committs.
The problem has solved independently of this change so this is re-enabled.
Tested with 8p.
Non-buffered sendrecv_rvec on domdec

Replaced sendrecv_rvec by the non-buffered version in domdec.
The fr->f_novirsum normal srealloc has been replaced by its symmetric counterpart.