trafgen: Fix compiler warnings

Fix the following compiler warnings that occur when building with "-W
-Wall -Wextra":

trafgen.c: In function ‘timer_elapsed’:
trafgen.c:136:31: warning: unused parameter ‘number’ [-Wunused-parameter]
trafgen.c: In function ‘apply_csum16’:
trafgen.c:346:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
trafgen.c: In function ‘dump_trafgen_snippet’:
trafgen.c:415:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
trafgen.c: In function ‘xmit_smoke_probe’:
trafgen.c:490:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
trafgen.c:506:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
trafgen.c:509:56: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
trafgen.c:512:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
trafgen.c: In function ‘__wait_and_sum_others’:
trafgen.c:721:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
trafgen.c: In function ‘__correct_global_delta’:
trafgen.c:743:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
trafgen.c:761:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
trafgen.c: In function ‘xmit_packet_precheck’:
trafgen.c:797:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
trafgen.c:816:47: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
trafgen.c: In function ‘main_loop’:
trafgen.c:837:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
trafgen.c: In function ‘main’:
trafgen.c:1047:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
trafgen.c:1065:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
trafgen.c:1078:43: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
trafgen.c:1090:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>