msc: split off f_mgcp_find_param_entry()

Split f_mgcp_find_param_entry() out of f_mgcp_find_param() to be able to act on
an MgcpParameterList without an enclosing MgcpMessage.

Will be used by upcoming I8b82476f55a98f7a94d5c4f1cd80eac427b2d20f

Change-Id: I90f213d2a1be979afa024e0faa25d532f9858636
1 file changed