AT#SRECV returns ERROR when reading too many data

AT#SRECV returns ERROR if too many data is expected. Based on [AT commands doc](http://www.multitech.com/documents/publications/manuals/telit_3g_modules_at_commands_reference_guide_r9.pdf) 1500 is the max size to read.

Handling many AT#SRECV within MTSASInterface::socket_recv, in case size is bigger than 1500 might be a solution.

Same limitation happens with AT#SSENDEXT in MTSASInterface::socket_send.

Read MTSASInterface::socket_recv and MTSASInterface::socket_send, then consult the linked Telit 3G modules AT commands reference guide for the 1500-byte limit on AT#SRECV and AT#SSENDEXT. Reproduce the behavior with data larger than 1500 and verify that the methods handle it through multiple AT-command operations without returning ERROR.

Written by the indexing model from the issue text.