dabba: merge all rpc header print functions.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
dabba: fix rpc header title typo

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
dabba: refactored rpc call function prototype.

RPC call function prototype have been redesigned to split the connection
from the RPC call itself.
Preparing the connection beforehand allows to tune it before executing
the call.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
libdabba-rpc: move rpc define to its library.

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>