The rdma-core driver.h include is no longer installed:
56dd87acd2
So ibv_read_sysfs_file() is not defined. As the symbols is still
distributed, we simply add the missing prototype manually.
Similarly, the gaspi_size_t gaspi_get_system_mem() function is not
available from the gaspi public headers, so we define it in the
max_mem.c test.
Fixes: #7
