virtiofsd: Changed allocations of iovec to GLib's functions

virtiofsd: Changed allocations of iovec to GLib's functions

Replaced the calls to malloc()/calloc() and their respective
calls to free() of iovec structs with GLib's allocation and
deallocation functions and used g_autofree when appropriate.

Replaced the allocation of in_sg_cpy to g_new() instead of a call
to calloc() and a null-checking assertion. Not g_new0()
because the buffer is immediately overwritten using memcpy.

Signed-off-by: Mahmoud Mandour <ma.mandourr@gmail.com>
Message-Id: <20210427181333.148176-1-ma.mandourr@gmail.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>