unit: Add {TEXT,URL}_STR{8,16} tests for sdp_extract_attr()

These tests are for valid data. Other tests might be added later to
check for error paths, but will require separate macros.

{TEXT,URL}_STR32 cannot be tested with the same macros because
sdp_extract_attr() does not support them. They will be tested
separately with other SDP library functions.

As example of failure output, if commit
504a0cf46ad89cab8005ce9cffb22e41048f6a30 is reverted for testing, the
STR16 test will fail with:

ERROR:unit/test-sdp.c:776:test_sdp_de_attr: assertion failed
(test->input_size == size): (7 == 11)
unit: Add tests for SDP integer Data Elements

SDP_DATA_NIL does not have a value, but its sdp_data_t val field is
zeroed by memset(), so just treat it as UINT8 with zero value to
simplify checking (and not require a separate macro.)

SDP_BOOL is handled by SDP library as a INT8.

SDP_UINT128/SDP_INT128 are just byte arrays converted to host order, so
use memcmp() to compare them (converting from host to network order
first.)